Is it normal?

Have you ever experienced sitting quietly without thinking of anything when you suddenly feel your emotion turn from blank to pure anger against everything around you or the world or even existing itself. If not rage, then maybe from blank to deep sadness (I can't really say if it's depression or not...), like you just feel empty inside out of nowhere and you just start looking at tall buildings thinking what falling position would let you die the most painless way possible.

So yeah, is this normal or should I be concerned? (Though chances are no one will see this. Meh)