Random HP Regen in OFA Yasuo

I'm not certain what happened, but my HP regen randomly increased from 17 to 225 after reaching > 10% HP. This happened twice in game. I'm fairly certain this was a deciding factor in at least one of those fights. Items and masteries didn't affect this; I had PD, Mallet, and IE I believe at that moment with Warlord's (18/12/0). Not sure what happened, but it was really dumb. Regen also didn't seem to be based off missing HP, maintained like +22 every second to my HP.

Also we didn't have any dragons at all, so it wasn't like 3rd ocean.