This is all good advice but trust me I've been retracing my steps this whole time. Besides that I specifically remember doing two quests
I did one that involved taming a spider, a nightsabre, and an owl. This quest taught me tame beast and a few other abilities.
After that I did a quest where I had to go speak to a hunter trainer in Darnasuss. I spoke to her and I learned 4 more abilities, including revive and feed pet.
I seriously think this is a game glitch, and if you look at the Help menu there is a category that is specifically for lost abilities. But until I get a GM response I'll be talking to every hunter trainer I can find :/