Those of us with Addison's Disease have or will learned to be cautious when exposed to high temperatures. We just don't handle heavy sweating and salt and potassium loss. It is a balancing act to keep the two in the right ratio...drinking too much without enough salt and we flush ourselves out. If we are taking fludrocortisone this helps to retain sodium but can lead to low potassium. Some have to really watch the potassium foods they consume as they tend to have high potassium. As I stated: it is a balancing act! Not always easy...but necessary to live well with Addison's.
I love warm weather but I can't take the heat! So I stay inside a lot! Or time your outside activities to a cooler time of day. It's all about compromise and knowing what your body is telling you. Getting overheated can be very serious for us so take measures to protect yourself from the heat of summer.
Drink lots of fluids and get enough salt to insure you enjoy your summer! And if you need to keep your potassium levels up, a banana or tomato can be a good option there.
Have a great summer!