WHY AM I OUT OF MANA! OMG!
 

A) You are out of food or water. If you get food and water, right click it to force consumption.

You are not actually losing mana.
The client just thinks you're gaining mana that you really aren't.

B) You've trained meditate before you were actually supposed to have it (most likely with the unsupported SoF client).

In this case, you actually will lose mana. All mana gained while sitting will be lost, including your base 1 mana per tick. You're stuck with standing mana regen until you get meditate at the correct level.

As of the next update, Haynar should have some major improvements to both of these issues.

From patch notes, both solved, so sticky might be superfluous. Course I haven't personally tested either.

Yep. Haven't gotten a single "Dude, where's my mana?" petition since the patch. Moving to resolved.