Im burning this swing

I'm in a panic right now, I feel like a POS Mom. My son is 11 days old and loves the swing and its been a life savor with a 16 month old running around. Well my 16 month old woke up from his nap so I went to get him out of his crib and give him milk. I went back into the kitchen after and saw that my newborn was still fast asleep just like I left him swinging away. I turn my back to clean out my older sons sippy and put water in it because hes done with his milk. I hear a odd grunting turn and my newborn has managed the muscle to try and sit up but cant hold himself up so he has slumped over and his face is turning red as he cant breathe. I of course bolt over and grab him already crying. He seems fine but I am a mess. What if I had been in my toddlers bedroom when he did that? What if I hadn't heard him grunt? What if he hurt his back or something else when he did this? My mind is racing. My son is never going in that damn swing again.