Bike broke down yesterday, working again today, need help figuring out why and if I need to do anything

Hey, just looking for a bit of guidance here. I'm a beginner-ish rider with little technical motorbike knowledge and terminology so I'd appreciate some insight. I know the initial reply is going to be "get a mechanic to check it", but I live in a country where I am not a native speaker of their language (Vietnam, I'm British), and I don't have enough technical vocabulary to properly describe the issue, so I want an idea of what I need to get checked before I go. Also in Vietnam, generally people who fix things for you don't tell you what was wrong with it or give it any explanation, they kind of just sort it out and you go (worryingly, this also includes things like doctors). I have no idea why but that's just how it is here, so I'd rather go in with some idea of what's wrong.Yesterday my bike broke down while I was driving home in the rain. At the time I thought it was because I over-revved it (panic switched down because a taxi pulled in front of me and stopped). Pretty shortly after that happened (don't remember how long but less than a minute), my bike shut down. I thought it had stalled so I shifted down again, still moving, and restarted. It immediately felt less powerful and eventually shut down again a minute or two later, I stopped at the side of the road and couldn't get it to start again. Decided to walk it to the nearest mechanic, once I got there about 5 minutes later I tried to start it again and it went, but was less powerful. Managed to get it home with a couple more stops. There was steam coming off the engine the first time I stopped, but I wasn't sure if that was evaporating rain.I took it out a couple of hours later to test and it drove without shutting down but felt significantly less powerful. Today I drove it about 15km with no incidents, but it might have lost some power - I'm not sure if it's just in my head though. It felt a bit weird in the low end, particularly in 3rd which is the gear I stalled in. Felt less weird the longer I rode though so it could be imaginary.So what my googling and common sense deduced is that it's either over-revving that killed it, or water in the engine. Since the problems have mostly (or entirely?) gone away, now I'm thinking maybe it was water, because google tells me that over-revving fucks something with the valve train and that doesn't just fix itself.It's a custom built bike btw so I have no manual or whatever but it's Vietnam so replacement parts and work are way cheaper than whatever they would be in Europe.Should I be worried about anything blowing up and what should I ask the mechanic to check? I do have another bike to get around with in the meantime, I just wanted to give it another go today and wasn't intending to take it far but it felt ok so I did.Thanks via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/dqhadt/bike_broke_down_yesterday_working_again_today/?utm_source=ifttt