1) bitcoin value goes up and down, so does everything else. Live with it or dont use it.
2) Storing your bitcoins on a server owned by someone else is like giving your cash to someone you dont know. Maybe it will still be there, maybe it wont. If you are on Linux, or Windows or OSX, use a client like electrum (electrum.org). You can store the bitcoin wallet on your own computer, without relying on some not so trusted intermediary. You do do backups dont you?
Yesterday I transferred most of my bitcoin stash (~$500 Aussie) into my own wallet on my own computer, and backed it up elsewhere.
The bitcoin is now safe, the value of it may change up and down. Bit like owning shares, isn't it?