I had what you'd probably consider two incidents. One was optical neuritis with lesions on the brain and the other was new lesions on the brain. Your MS sounds very mild(fingers crossed) like mine(other hand's fingers crossed(wait how am I typing lol)). Personally I was not sure what was going on with me for quite a while and I continued my regular activities. A year later I've noticed that it is a bit harder to maintain my fitness(I am still able to run though) and I've been forced to cut back the intensity of my runs because I get quite fatigued and a little woozy. As soon as the runs are over and I start to cool down I feel a lot better. I wasn't able to do much but swim this summer because the heat has started to get to me. I'm able to operate normally but it drags down my energy and motivation and makes me feel groggy.
To answer your question from my experience, which as someone else mentioned is unique and could have no bearing on yours, the worsening of symptoms caused by heat and exertion is only temporary and leaves no residual effects. It may leave lasting damage if you really push it, for example trying to run a marathon in 90 degree weather or something.
All in all I'd actually push for further research into the cause of your problems because the sooner you get a diagnosis the sooner you can start some type of treatment if needed. Some will argue that the "preventative measures" like Copaxone, Avonex, Beta seron, etc. don't help but I really feel like mine has kept me almost entirely symptom free for a year even if it's just in my head(optimism is key!). In the mean time take special care of your diet. Don't do anything extreme but try hard to stay away from processed foods, hydrogenated oils, MSG, fried foods, and other unhealthy things. Take a multi-vitamin or figure out which supplements would be best for you(Jimmylegs is the expert). A big thing for me, as I mentioned, is keeping active. If you can manage it exercise when you can, you don't need anything intense but staying active really keeps your body functioning right and will definitely help your body maintain itself. These are things everyone should
do but when something like MS is thrown at you, or even a scare, you realize that you have to take special care of your body.
Sorry for the sermon. Good luck with your continuing medical search.