Have you tried logging out and back in? Maybe whip in and out of the transform, then redo chest piece?

Also, FYI, with 870 toughness on my character, I get to 27k health (I stripped off any health gear, which also stripped some toughness). I'm not sure what tougness 916 should give you for health, outside of health stats on gear. Are you sure you didn't remove any gear w health bonuses on it? Skill tree choices will also affect your health.

If you completely strip your character, what is your toughness, and what is your health number? Note, some passives you or I have can make our numbers completely different though, even with same toughness. Check your skill tree too. I'm not sure, but there might be one that even lowers HP in there in order to gain damage or something.. like a glass cannon type skill. I'm really not sure on that though, I'll see if I can find one.

Found one passive... Dire Juncture in Time Weaver (purple outer ring) is one that really lowers health and force shield (not by half, but still might be a factor here). Do you have that skill?

A portion of the damage you receive is delayed, and this delayed damage does not interrupt Force Shield regeneration.
Your maximum Health and Force Shield is reduced.
You only take 40% Damage of an Enemy's attack when it Hits, the rest is inflicted is after the Hit
Your Health is set to 85% of maximum, and Force Shield to 85% of maximum