5 month old hyperventilating

So my baby boy was recently constipated and hadn’t had a dirty diaper for a good 3 days. Today, like 10 minutes ago, he was grunting and I can tell he had pooped but he started to take very quick and short breaths that I can only assume was him hyperventilating. I picked him up immediately and he stopped. I was so afraid something was wrong. I changed his diaper and noticed his poop was slightly turning solid from the cereal I’ve been giving him. So maybe that may have been a factor? Would like your thoughts, mamas!

Edit: The cereal is actually oatmeal (single grain cereal)