Parenting is so hard

Yesterday my LO had a huge meltdown OUT OF NOWHERE. He was smiling at the ceiling on his boppy and then just started wailing. I didn’t know what was wrong, it wasn’t hunger or anything so i am sitting there almost in tears myself cause I have no idea what’s wrong. I remember reading on here that skin to skin helps soothe them so I immediately tried that and he was calm in seconds. But I felt so helpless and the fact that I don’t know what caused him to just cry out like that has made my stomach knot up. As FTP, my husband and I are always on our toes about everything and we realize that being parents is the most rewarding, hard, and loving work we are ever going to do.