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.

No it does not sound normal.

Other represents Cydia apps and also general iPhone settings/etc

How were you downloading and installing stuff?

There are two disk partitions on the iPhone, one is for the iPhone OS and the other is for your content. Cydia needs to install some things on the iPhone OS partition and it is quite a small partition so it can fill up. Cydia has a way to show you the usage on each partition. Cydia/Manage/Storage

Regardless, the OS partition filling up should not destroy your music library.

What were you installing?

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.