Anzu itself most likely, my feral gear (OS) is ~6k and I dont lose more than 3-4k HP, but the mobs before him are annoying really, just that one group that you have to clean, other you can stealth past.
That group I usually pop CDs on just to get it over with sooner, anzu doesn't require CDs, just pull him to one corner and you can take your time, kill him in 15s or in 15m, doesnt matter.
If you're SUPER low (like <10k HP) you might wanna go bear form and take it easy, you'll dodge most attacks anyway.