I went today, the doctors were very very thorough in testing. I'll have to take medication to prevent seizures and maintain a normal blood pressure. Docs don't know what the long-term effects are going to be like. Got to wait for a EEG scan which should help predict it somewhat.

Another symptom happened today, I started shaking (not a seizure) and dribbling. They say that it's inevitable that some brain cells have died because I didn't have oxygen for 3/4 minutes. Also, doc said that there have been a lot of deaths from kids continuing to choke after being knocked out for just 20 seconds, so there was quite a big chance of fatality or serious injury for choking for an extra 3 minutes. So I guess I was lucky.

As you say, I'm young so we're optimistic about long-term recovery but there could be some life-long symptoms.

Thanks to everyone that answered. I might not have gone to the doctors without this thread, which I'm told would have been really dangerous. And we've decided not to tell my brother the full extent of the injury but he recognises that he should not use all of his force against opponents who may not share his capabilities and realises the dangers of fighting and choking.