Decide to come clean, and ask some pressing questions

"So uh, this will sound kind of unbelievable and straight out of a movie, but... I had this really weird dream."

You have your family's full attention. Even your stereotypically snarky sister keeps quiet, probably sensing that there's a grave matter afoot.
After a pause, you continue.

"So I don't even... I don't even know what really happened, but basically I have... memories. Or, uh... Maybe not memories but I can't get the idea out of my head that people should be in toilets and not on each other. Not on women's clothing", you correct yourself.

A few blinks mirror those you blinked yourself a few minutes earlier in Lucy's bedroom. Your mother is the first to manage some kind of reply:

"Where is that coming from? Why would you hog the toilet like that?"

"Why would you even want to piss in such a nasty place to begin with.", continues your dad.

"I don't know!", you counter. "I don't know how it works in your world, bu-"

"Excuse me, in our world?", interrupts your mom, understandably upset at your poor choice of words.

"I... Uh... Alright, promise to not put me in an asylum?"

"I mean it's kinda late to do that anyway", Lucy snarks.

"We promise", your mother assure, to which your father raise an eyebrow you'd rather not have seen raised.

"Alright. Alright. So. I had this weird dream. In it, a strange voice told me that from now on, people's peeing habits would change."

A look of understanding pass on your father's face. "And that's why you got it into your head that people should pee in the toilet? Because of a bad dream?"

"Well... no", you answer. Oh god this is gonna be awkward. "It tried to get in my head that people should pee on women's clothes."

Your parents look dumbfounded, and it takes your modernly savvy sister to save you from further embarassment: "Wait so you woke up thinking that not only people should, but people have always peed in the toilet, and all of this is... is new to you? Like you've woken up in another dimension or something?"

"YES!", you almost scream, delighted to have your situation put into words. "Yes, that's exactly that."

"So mind explaining why your first reflex was to come piss on me then?", your sister snarks.

You should have known there was a catch. And boy oh boy you won't stop hearing about that one. "Well... uh... My body seems to know what's going on. Like I've got the right instincts. It's when I realized what I'm doing that things get messy in my head."

Your sister smiles a mischievous smile. You dread to think what she might do with this knowledge. Fortunately, the time is not right for sibling rivarly hijinks. As your parents finally recover from the bomb you've dropped on them, your father starts talking:

"Are you sure you don't want to see a doctor? Sounds to me like you've got something messed up in your head, boy."

"No no no no no, that's really not necessary! I mean, besides the whole piss thing, this seems to be pretty much the life I had. Hell I'd bet my left hand that my saves are exactly in the same state I left them yesterday."

Your parents look at each other wordlessly. Obviously, they're mulling this over. A tense awkward moments later, your mother finally speaks:

"Alright, we're going to trust you on this. This is a lot to take in, and I'm still prety convinced you must have bumped you head on something... But if you're willing to try and fit in, then things must be at least kind of alright in your head."

Relieved, you throw yourself in your mother's arms... and quickly recoil with disgust when you feel some of her freshest stains transferring to your own pants. Which prompts your mother for one the most awkward lines in the history of awkward lines:

"Oh. If you want to fit in, someone should probably explain to you how things work, now."

You gulp, sensing a very unusual version of The Talk™ coming up.

About half an hour of you being embarassed, Lucy giggling and your parents doing their best to quiet her down while answering to you as honestly and earnestly as possible pass. Once you're finally through this hell of a briefing, you look down to the rules you've jotted down.

• Piss is supposed to go on women's clothes.
• Most men keep some women panties in their bags or pockets in case the need arise and there aren't any women nearby.
• It's preferrable to pee on a naked woman rather than an unworn pair of clothes. ("How COULD you end up in such a situation?", your mother asked to this one, to which you're pretty sure that your sister blushed.)
• Unless it's in the shower. You're supposed to piss on women's clothes outside of the shower cubicle if you're ever in such a situation. ("Wait, why?", you asked. "Because peeing in the shower is disgusting!", your mother answered.)
• Pissing in the toilet is considered as hogging the toilet, and a bit nasty ("compare pissing to eating", you've noted down, in order to get how common a thing it is to do in various places and situations).
• Since the need to piss is much more frequent than other bodily functions, you're fully expected to piss even during the most formal of times.
• Yes, that includes meetings, speeches in public, while being onstage and such.
• No, there aren't dedicated "urinal workers". ("Why would we even need those?", asked your father, to which you're shrugged.)
• On the more biological side of thing, women's sweat is toxic to most bacteria that usually thrives in urine, and human skin isn't suscpetible to rashes or other kind of sanitary problems that should arise when one keeps wearing piss-stained pants for days. (You kinda chuckled at the convenience of that. But then again, you remember that Mother Nature gave most animals a copy each organ "just in case the other breaks", which is just as contrived coming to think about it.)
• Yes, you can piss wherever you want on women's clothes. It's appropriate to focus the groin area, since that's where they're going to piss themselves anyway.
• Depending on the woman, she may or may not accept you to piss in her hair. (This one puzzled you a lot. Hair is supposed to be kind of like clothes, so apparently this could make it okay for some reason.)
• As long as it's regularly used, it's okay to relieve yourself on a woman's bed, shower towel, backpack, or anything that's usually close to her skin.
• Human metabolism apparently goes faster. (This one in particular didn't come from one of your family members: rather, you noticed that everyone at the table had to go during the half-hour you spent learning how to fit in, three of which you knew had already took very long piss less than an hour ago.)
• You shouldn't go to the toilet for #1, even at home, in order to chase your old habits as fast as possible.
• No, you don't need to ask for permission first ("..., you dimwit", Lucy snarked when you asked her whether you could relieve yourself on her since you've just been denied acces to the toilet.)
• Yes, this does mean you can piss on passed out/drunk women. ("I mean it's not like you're abusing them or anything". Right.)
• Yes, somehow managing to not piss on women will be seen as weird by all those that notice what's going on.
• "Washing your hands" is called "rubbing your hands on a woman's clothes, probably the one you just pissed on".
• "Wiping" is called "wiping", except it's done on and/or with women's clothes, same as with what would normally be "washing your hands".
• No, women's clothes aren't used for anything else. ("What, you weren't thinking of creaming my panties or something, were you?", Lucy joked. To your surprise, you feel just a hint of disappointement.)
• Sexuality, and more precisely women's genitals, are much less taboo and much more of a casual subject of everyday conversation since most women don't even bother with actually wearing panties anymore.
• Most women don't even bother with actually wearing panties anymore. (This one you had to do a double-take on.)
• Most women wear skirts, yoga pants, or whatever is comfortable when going pantiless as a result.
• Most of what would've been considered harassment, invasions of privacy or perversion in your old world plain isn't here. This include, but isn't limited to: staring inside a girl's skirt (panties or not), sharing fantasies with them (whether about them or not), commenting on their genitals, going through their drawers, asking whether they're wet (though this might not be the kind of wet you were thining about).
• Breasts are still very much sexualized and still the subject of harassment and stuff. Same goes for voyeurism: be caught as a peeping tom and you'll be in real trouble.
• This also doesn't include sex acts: having a raging hard-on in public is socially acceptable, but masturbating with an audience isn't.

You still have about a thousand other questions, but time didn't wait for your shenanigans, and before you knew it, it was time to get to school.

Just outside your door, your sister calls to you from behind: "Oh, wait a sec."

Turning back, your face goes red as you see what she's doing: she's taking off her pants, right there, for the world to see! You're surprised to notice she wears panties, after all the fuss about them being unnecessary and stuff you thought she wo-

"Here, take this. They're freshly worn."

Lucy chidishly sticks out her tongue to you as she puts her yoga pants back on and resume walking to school. You're left dumbfounded, having just witnessed your sister's pussy on full, nonchalant display, a pair of freshly worn panties in hand. And as you start catching up to her, you can see her grey yoga pants quickly darkening as she's very obviously making a show of pissing herself in front of you, complete with "Aaah, that feels better!" and other toilet-related commentary.

Oh bother. This is not going to be easy.