Why won't my iPhone screen rotate sideways when I rotate my iPhone?

I know this is the wrong section but you guys are awake and this is serious.

Ok so I asked one of my friends about it and he said that the screen lock might be on. So I a checked information ok the screen lock and found out what it was and everything and turns out my screen lock isn't on. If it was on that twisted arrow thing was suppose to show at the top right hand corner of my phone.

I DOUBLE TAPPED THE HOME SCREEN BUTTON AND THEN FLICKED TO THE RIGHT AND KEPT LOCKING AND UNLOCKING THE SCREEN AD IT STILL DIDN'T WORK.

So since it isn't the screen lock can any one give me any advice on how to fix this problem. Oh yeah and one more thing, I dropped my iPhone so I think that could be it but my iPhone is working fine it's just that one problem.

Btw there are some games where you can only play sideways and it works for those games but that's because in those games you can ONLY play sideways.

I have a strange feeling it has to do with me dropping my phone but everything else is working fine.

So I would really appreciate it if you could help me.

Before you answer my question re-read the 3rd paragraph.

Added (1). @ Dreamstuff - Only tilt based games work but that's it. Even YouTube videos won't tilt.

Try asking someone at the apple store or restart your phone

Maybe the screen lock is on. Or maybe Satan is responsible.

It's broken because you touch yourself at night.

Because its made by Apple

Does the accelerometer (or whatever Apple uses) work? Do tilt-based games work fine?

Double tap the home button. A small box will raise up. Swipe to the right and you will see something that looks like a lock. Tap it and it will turn that off.

On the new iOS system just swipe sceen upwards and you will see lock screen icon at the top (circle with arrow). Click on it to unlock.

Yep swipe up lock button in R. Hand corner tap to lock& unlock.
I just did it & it worked

Go about it like you're turning your flashlight in and up in the right there will be a lock symbol just hit that.