Cry it out😭

We are having a terrible time getting our 5 month old to sleep through the night (or even sleep more than 3 hours at a time at night). Tried Ferber, but what Ferber does not cover is what to do if your baby simply does not stop crying on his own. It seems that my son's crying only promotes more crying, like a snowball effect. He cries so hard it's like he's in a trance. I have let this go on for more than an hour, but I intervene for fear that he is going to hurt himself.

So if crying it out doesn't work, how can we manage to get a decent night of sleep? I figure between a crying baby and a miserable pregnancy, I have not slept in about 14 months