My Barb's mana is going up and down when he just stsands still, why would that be ??

frostmourne
cowset
bulwark
lk belt
soj
cain ring
rising sun
hysteria
(torch anni belial prime)

As i wrote down this, my barb went from 312 mana (full mana) to 50ish, now it goes up and down. weird !!