When does the health bar appear over enemies?

I noticed when you get into combat, a little red HP bar appears over each creature in combat, both friend and foe. However, it doesn't seem to appear over every creature, and occasionally it will dissappear.

Does anybody know what the exact trigger to get this thing to appear is? and when does it go away?

its really useful to pay attention to those things, that way you can see more than one person's health at a time... especially as a spiker... when you want to wait 'til he gets pretty low and then nuke him ded before he gets a chance to heal.

But i'de like to understand better when they appear.

Is there a way to force it?

If the enemy/ally is at full health, no health bar will appear, but if they take any sort of damage, the health bar will show. If they heal all the way back to full health, the health bar will disappear.

from my experience, sometimes when the health bar appears on foe, the bar would be empty even though it has full health. and when you're attacking it, you have no idea how much health the foe has remaining because the red color isnt there.

i dont know if this also happens to other people, but sometimes i cant use any skills or spells on an enemy during combat. and yes, i have full energy. while im attacking it, each time I click on any skill or spell, it would just simply refresh itself and nothing happens. this goes away after i killed the enemy. this thing happens occasionally.

i dont know if these things are bugs or is it just that i am lagging???

I noticed that sometimes as well.