I think this depends on what you normally do. I go to the gym every day and do weight training and running. Since I am eating less, I will probably do less, but since I am in the gym, I can stop anytime if I feel light-headed. On the second day of the programme I ran 10km in the bush at my usual pace.
If you usually exercise vigorously then just be careful and listen to your body, and do something that is not too committing so you can stop and get home easily, or sit down or whatever. if you are not used to exercising, then it is ALWAYS important to set off gently and gradually build up so that you avoid injury.
It also depends on what you like doing. Walking is always a good bet. If you are not sure how fast or far you can go, then find an oval, or just walk a short distance then return, then repeat, so that you are always near your starting point. If you let me know what you usually do, then I am happy to make some specific suggestions. Look forward to hearing from you.