Lose life while alt+tabbed in Eternal Laboratory (and other areas)

I was in The Eternal Laboratory when I first noticed it. Since there aren't any mobs there, I shouldn't be taking damage. I have a Righteous Fire character with just over 7,000 health. I'm healing about 130 life per second over the RF damage, so I have no trouble using this character in maps. Whenever I alt+tab to surf the internet, I come back to see that I lost about 1,000 health.

No matter how much time I spend alt+tabbed I only lose about 800-1,200 health. It seems to be a random amount, even between areas. In the Library I lost a little more health over a shorter time than in the Eternal Laboratory, and in the City of Sarn it was less.

My guess is that some of my gear is getting disabled, or maybe an aura isn't functioning while alt+tabbed. If this is true, then this is a problem that isn't specific only to Righteous Fire characters, but a problem to anybody using the same items.

My auras are: vitality, purity of fire, and determination(although that doesn't affect RF)

Here are items I have in case that's the problem:

gonna take a guess and say it's something to do with low fps while alt tabbed?

I don't see how fps could affect my character losing health. But in case it did I went ahead and tested it out with a few other characters, and they were fine. Only my Righteous Fire character lost health.