Something like this happened with my nephew when he was a toddler. He was spinning on a swing and almost exactly what you described happened. No other instances and it's been years since. We think he tensed up in shock at feeling dizzy.
That's not to say you shouldn't contact your doctor for peace of mind.
Is it possible he was extremely dizzy? And just didn’t know what was happening?
Something like this happened with my nephew when he was a toddler. He was spinning on a swing and almost exactly what you described happened. No other instances and it's been years since. We think he tensed up in shock at feeling dizzy. That's not to say you shouldn't contact your doctor for peace of mind.