Where is the DMG coming from? (Death Recap)

Why when I play a tank mostly Maokai , when I look at my death recap and I somehow get burst down in three seconds by the enemy team the death recap dmg says I took 2900ish dmg in 2.96 seconds. Which means I took that amount of dmg and died, but when I look at my health bar and see I have over 4000 max health. Meaning threw some magic that cant be shown I took about 1000 - 2000 extra dmg somewhere and the game can't tell me why. Knowing where the dmg came from would be useful so I can know what to build, but the death recap also only shows three people and doesn't say all the dmg they did either. So where does the extra 2000 dmg come from that the game says I didn't even take?