This is the effect of battle leveling. You get a major boost in health and your attributes get adjusted in a somewhat arbitrary manner. It happens to anyone under vr14 but I believe you can turn it off
As it stands right now Battle Leveling ignores builds. This will be fixed with Orsinium, if I recall correctly. If not Orsinium then the next DLC.
As for Health it is Battle Spirit, as Danny pointed out. Read the description in the Character Menu for information on Battle Spirit, which displays there while you are in Cyrodiil.
Guildmaster of Power With Numbers in PS4 NA Server's Aldmeri Dominion.
Proud Founder of the Yaysay cult! DOWN WITH THE NAYSAY CULT!! #ToxicRemedy