Toddler hit head, and I am a bit nervous!

I have a 22 month old. He has a bad habit of throwing himself backwards when playing or throwing a tantrum. We were on our bed and he was playing with his father. He got excited and threw himself back. The back of his head landed right on my kneecap. He cried for a couple minutes, and I fell to the floor in pain. My knee is super sore right now. He didn’t get a bump, and he acted fine afterwards. He was actually a bit sillier than normal. It was right before his bedtime. GO FIGURE. He fell asleep fine, but now I’m freaking out that he’s hurt. Could he have hurt himself that back from bouncing off of/hitting my kneecap? I mean my kneecap is straight bone. I know this may be ridiculous to some, but just looking for SOME reassurance. UGH! 🤦🏼‍♀️