When should I let my baby 'cry it out'?
It depends on the age of the baby. In the first two or three months of life you can’t spoil your infant, so by all means pick them up, walk with them, calm them down.
After that let them begin learning how to soothe themselves. If you know they’re not wet, not hungry, and nothing else is wrong, let them cry a while and blow off steam. It’s OK to put them down and give yourself a break. Just leave them in a safe place and give them a little time.
What do I do if my baby cries so hard they seem to stop breathing?
Crying is not dangerous to your baby. It’s not going to cause brain damage and they’re not going to stop breathing. There is, however, something called breath holding spells, where a baby may cry so hard that they stop breathing for a moment or two and then start breathing again. If this happens, you do want to see your pediatrician to be sure nothing else is occurring. If they really seem to stop breathing or turn blue, call the doctor. It could also be that the baby just cried so hard that mucus got stuck in their throat.
Breath holding usually applies to toddlers. Some hold their breath until they pass out, and of course it really upsets the parents! It’s not very common in babies, but I have seen it. It’s not dangerous but it can be scary for parents. Children do grow out of it.