@Manul Otocolobus
Maybe? I was ridiculously fit at one point not so much right now (got sick last few months). I could never do a lot of "cardio" before being extremely out of breath with shooting chest pains, much better at short distance sprints. Swimming and firefighting A-OK though.
My parents told me it was normal due to family genetics. When I'm not sick I'm usually around 50-55 bpm even if not fit. "Supposedly" runs in one side of the family with asymptomatic bradycardia/hypotension.
A direct relative of mine has 90/60 51bpm with no symptoms. That's the side of the family with rheumatic fever.
Deconditioning once one is very fit will typically take years on end. I can't speak to the cause of the out-of-breath, but the chest pain is likely one of two things (since your heart checked out ok). 1) The nervous system sorta goes into overdrive when one is doing intense cardio, as a result it amps other systems unintentionally. That's why people who are runners can have explosive diarrhea suddenly even though they aren't ill. One system that gets stimulated unintentionally is the one that is responsible for acid production in the stomach. It can cause some incredibly severe acid reflux, which for some people is essentially indistinguishable from pain that is cardiac in origin. Taking some famotidine before cardio it typically curative. 2) Our thoracic skeleton doesn't have much articulation for movement, despite the fact that the chest needs to move for respiration. During rapid respiration, such as being out of breath, or during coughing (which some people do when they are out of breath) the joints that allow for movement of the thoracic skeleton, known as the costochondral joints, can become inflamed, and it can result in surprisingly intense chest wall pain. Common anti-inflammatories can help, but sometimes it is difficult to treat.
Since you have a history of being fit and given your weight, which is borderline for being underweight, benign bradycardia, and possibly benign hypotension due to the bradycardia, are completely normal. The potential genetic component is interesting. It is possible. There are a few known heritable conditions like that. As long as you don't experience any concomitant issues that are associated with bradycardia or possibly hypotension, I'd be unconcerned.
Interesting. The only insult I can think of is that I pulled very hot tea on myself as a baby and got 2nd degree superficial burns all over my torso, then the rural hospital my parents took me to put sticky dressing on which my parents had to soak off when they got home. GP said they put the wrong dressing on it.
I have extremely fair skin.
An insolated, moderate thermal incident, fortunately, isn't likely to be an insult to the skin, in general. The skin is surprisingly resistant to thermal incidents. Generally one would need to experience repeated thermal incidents over a long period of time to an area of skin for it to become an issue. Insults, in general may not be something of which we are aware or we don't generally think of as a potential insult. Air pollution, a medical chest x-ray, a chemical in a skincare product that turns out in the future to be a danger, etc... trying to estimate all the risk factors one is exposed to are just about impossible except for major ones, like UV radiation. That's why reasonable surveillance of the skin is the best way to catch anything that could be problematic. On a balance of factors, I'd generally trust a dermatologist one sees to make the right call on whether something is questionable or not. If one is really hesitant, active surveillance is always an option. This would be just to exam it at certain intervals and note any changes. If nothing changes, nothing is probably going on, since problematic nevi typically change in appearance in short intervals as their cell division is rapid. If anything changes, particularly significantly and suddenly, then that would probably tip the scales in favor of active investigation. With extremely fair skin, it isn't a bad idea to have a dermatologist that is known in your area for their clinical skill to do a skin check and proceed from there. If nothing is going on, you get peace of mind. If something is questionable, all the better to have to ability to proceed on doing something about it or proceeding with active surveillance.