The only way to get over a fear is to face it head on. A fear of sleepovers is completely irrational. Try slow and have one friend over to spend the night, do the usual sleepover activities with just the two of you. Once you see how fun that is the next time invite two or three people over. Youll see in no time theres nothing to be afraid of, sleepovers are fun.
i use to have this problem BAD. i would always go to a friends to sleep over and wuss out at like 2am, trust me my parents weren't happy with me. it gets better with age, once you get to a certain age you're going to wanting to be having a sleep over everynight to get you away from home, no worries!
Depends... what are you afraid of?