I ended up taking him to the doctor and he's fine.

Mainly took him in because I wasn't sure what exactly happened.

He was asleep in the swing and Noah was watching Mickey Mouse, so I strapped Oliver in and told Noah I was going to have a shower. Heard Noah run past the bathroom while I was under, which was kind of suspicious, so I turned the shower off and could hear Ollie crying. Got out, wrapped in a towel, thinking he'd spat his dummy out and woken up and he wasn't in his swing. (talk about a panic!) He was underneath it, crying. Noah must have unbuckled him to try to pick him up/ give him a hug.
So, because I didn't know if he'd lost consciousness (though I highly doubted it) I took him in. After waiting over 2 hours, finally saw the doc for all of 5mins.
But at least he got the all clear!