Flaky hitpoints?

I just noticed that my hitpoints were jumping between 399 and 437 - all on level 17.
There were no enchanments visible on screen and also no bonus caused by any kind of quest items.
Neither did I change my armor or apply any kind of upgrades, which would cause a hp increase.
So far the only difference I could see between those odd number changes were the different zones I traveled in.
Am I just seeing things here, or is there actually a small +/- modifier for health based on terrain/zone, well basically s.th. non enchanment or quest item related?

Everytime you beat a boss mob (with the cool glowy effect) you get a +2% modifyer to you HP and energy. You can get up to 10%. In some missions there are other ways to raise this modifyer as well, like killing certain non-boss mobs and completing mini-objectives. Also, when you die, you get a -15% penalaty and this can stack to as much as -60%.

There must be something going on. With no HP modifiers, as far as I know, the HP for level 17 should be 440. So if you have less, I think it would have to be from a rune used in an item along with a combination of any other HP modifier, such as morale boost, death penalty, enchantments, or item mod.

DOH!
I completely forgot about the morale/death modifier, which could have been the cause for this.
...and there I was hoping for a tiny hp bonus in elevated positions

Another possible explanation relates to special quest items that you hold in your hands and can drop, often for special effects (AoE slow, bleeding+cripple, knockdown, +10 energy, etc.). While holding them, you're NOT weilding your weapon set.

weapon + shield/focus both with health mods: Pick up a quest item, and then you lose the health bonus.