D.W.
Almost all toddlers go thru this. Parenting doesn't stop at night. He is very young and it's part of our job as a parent to offer comfort and security and reassurance. It won't create a dependent child or bad habits. For no known reason my 28 month old had me up *6* times the other night. I finally slept in her room with her and she settled right down for the rest of the night. That's all she wanted/needed. Me, some reassurance, whatever.
And if you are going to do CIO you have to follow the method (I shudder even typing that because CIO will never be done in my house). You don't leave them to cry all alone. That teaches them nothing about sleep, getting back to sleep or self-soothing. And what a horrible thing to allow-they throw up or poop because they have been crying so long!? That's not the kind of night i want for me or my kids.
Sometimes toddlers just need their parents in the middle of the night. Just reality. Don't you ever have nights where you don't sleep well? Have gas, belly ache, wake up thirsty, toss and turn? Same with them. Except they don't know what the heck is going on and they turn to the one thing (crying) that will get them the person they depend on most-mom and dad.
When mine are having an off night I go in, assess what's going on-bed not wet, no fever, etc and then offer "mommy's here. shhhhh. time for nite nite" and get them settled again.
It will pass.