somethings wrong about mana and energy shield

I keep getting killed by monsters that seem to bypass my shield. Normally, damage should hit my mana first before affecting my health, but in this zone, there was one time when everything was full, yet the damage just directly hit my health. Also, sometimes, while I’m fighting monsters, I just die randomly, and it says 'committed suicide.' What could be causing this?

Are you using a mana flask that removes life from you?