The things that are written here are not a recommendation of any sort. This is only an account of what seems to work for me in controlling AFIB.

Concerning dehydration, I make sure to drink water, cold water if available.
Concerning the possibility of electrolyte imbalance, when I was in the hospital, tests returned in normal range.
I probably use more salt than my doctor would approve of. I take OTC magnesium and potassium supplements every morning because of long term leg cramping issues. Periodic blood work continues to show electrolytes in range.

I have two truggers. Stress and heat. I have a tendency to be a highly (hyper) focused and intense person. I have had to learn to moderate that intensity.

Whenever there was an event, I review the last several hours. I look for things that may require modification. What did I eat. What did I do. Where did I go. Who did I interact with. What were those interactions like. What demands were placed on me. What was or is my stress level. How strenious was my activity. What was the heat and humidity. What were my thoughts and attitude. When did the event start and what was I doing immediately prior. How did my body feel. Did I wait too long to go get cool.

This is what I do.
I avoid eating too large of a meal. On days when there is a mid morning or afternoon energy lag, I will get a protein based half-sandwich and glass of milk.
I take magnesium, potassium, and multi-vitamin supplements in the morning.
I take a blood pressure medication in the evening.
Soft drinks are avoided as the go-to drink. They are occasional. A six-pack may last us two months.
I avoid Gator-aid because of the high sugar content.
I am more deliberate about getting good rest and not staying up excessively late. If I feel tired during the day, a 15 minute snooze helps.
My shop office is air conditioned and has an old recliner where my pup and I take an afternoon nap after lunch when temperature allows that many hours of work.
When working, I take cool down breaks, in AC, and drinking cold or ice water or apple juice.
There are people and situations I avoid as much as possible, and some absolutely.
I added air conditioning to my 1978 Jeep.
If I feel an irregular heart beat, drinking very cold ice water seems to help reduce the intensity.
I take time in the woods, enjoying the sounds and paying attention to things I see. I enjoy inspecting the rocks in the creek.

When listening to my body as to when to quit, I usually begin to feel a bit uncomfortably hot. I feel my heart beat a bit more intensely. Even though I do not feel it yet, I begin to feel that if I keep going, I will become light headed. Sometimes, I find myself pausing, and taking a deep breath to regather myself before continuing. When these happen, it is time to go spend the rest of the day in a cool place.

The mental aspect for me is dealing with the restriction while maintaining cool space activities that are productive. I am still working on this.