Only mildly panic!

Amanda is just a few years older than you, but she's acted like she's your third parent since you were little. Everything you did, she had some criticism of. Everything you wanted to do, she implied you'd have to try harder to get it.

She's not a terrible sister... once in a while she's been willing to descend from her higher plane to help you study for some big test, or drive you to the mall to see your friends. But as the eldest she clearly had a lot of pressure on her from your folks to excel, and she's seemed frustrated that you and your brother were allowed a more lax upbringing... frustrated enough that she probably decided to take it on herself to make sure you're pushed as hard as she was.

"Amanda," you gasp, still trying to catch your breath because holy shit is that how orgasms always feel for guys? "I... I'm sorry, I..."

You quickly cover yourself up with the sheets that haven't been messed up, and goddamn that still feels good, your cock is slightly softer now but touching it sends a whole new kind of almost-too-sensitive pleasure racing through you. "I can explain--"

"Who..." Your sister's eyes grow less spacey as she blinks, daze fading as her gaze focuses, cheeks gone pale with shock slowly turning bright pink. "WHO THE FUCK ARE YOU?!"

"It's me, Amanda, it's Ellie... I know this sounds crazy but..."

Amanda is scrambling to her feet, gaze still moving from your face to your cock as her surprise finally fades. Not good, you have about five seconds before she runs off screaming for help or to call the police...!