Is this normal? Last night i went to a friends house and i was installing stuff with his wifi. I also got several warnings saying i have low on disk space but i had something like 8.9gb in my "About" Section in Settings so i ignored it. Later my battery went out so when i can bak home, i plugged it into my computer and i see that i dont have any video or music files on my ipod. The name of my ipod is now Untitled Playlist

Is this normal?

Also it says Other - 5gb in the memory bar thingo.

The low memory thing results from not moving your Applications directory. To avoid this in the future use BossTools, and tell it to move your Applications.
As to why it restored, I have no idea.