Sweetheart from what you describe, it sounds EXACTLY like he is teething. This doesn't have to be on the day he gets a tooth - it can build up for a week or several weeks beforehand - the teeth are pushing up through the gums, gradually.
It sounds exactly like my baby - he doesn't want to be put down to lie down, doesn't want to be alone, he is genuinely upset.
I think if you do anything that exacerbates his fear of being left at this point, it will not improve things.
Whereas if you work through it with him, not against him, it will help him feel more secure and that can only ever be a good thing.
You have got the answer - you have found something that works, which is to hold him and sleep at a bit of an upright angle, which you can gradually decrease as he falls asleep.
This is what I do - I hold mine, then settle leaning back on pillows then gradually as he settles into a deeper sleep, I go flatter till I am comfy enough to sleep and often he can sort of roll gradually into his own space next to me on the bed.
Then I can either get up and go to a different bed nearby or I can stay put. (am on my own so no husband rolling about 
)
It works really well. They DO get clingy when they are in pain. Leaving them to it, even going in every few minutes, isn't going to make them or you feel better. If you work with them through it, they will be happier and settle much better in a few days usually, it never lasts that long, not this badly anyway. You'll find you get good nights and worse nights.
That's Ok - it's normal and they grow out of it nicely when they are ready. I've never ever done CC or CIO and never tried sleep training because what a baby needs is obvious, a lot of the time - they stop crying when you've got it right!