> How long would you be comfortable fasting for without medical supervision?

One week if you don't have any major health issues.

Not even a day if you're suffering from some serious condition.

Plan for less physical activity than usual, but do not become a vegetable. Take some short walks, do some small work with your hands. Meditation is great during this time, but you have to be somewhat accustomed to it.

Restart eating step by step. Begin with some fruit juice or clear soup. Then graduate to very soft, almost overcooked rice or something like that. A vegetarian diet for the first few days is beneficial. The longer you're fasting, the more cautious you have to be with restarting your diet.