HP Regen Malfunctioning
I was in the Sewers when I swapped out my only HP Regen item for an item that had none. That meant that I had 0 HP Regen left. After receiving a few hits from rats, I noticed my HP was not going up passively. I experimented and took a few more hits and was left with that amount of HP, no increase. I decided to relog and started to receive a ton of healing, more than I've ever received before (around 4 per tick). As other players have mentioned, it might be from combat affecting the HP but before I relogged, I still should have been receiving passive HP regen.