Some people on the /r/fasting subreddit go on for 40+ days. I settled into intermittent fasting routine and stopped thinking about extended fasts. I might give it a try. 5 days is quite extreme too, for me anyway.
Intermittent fasting is my go to regime to keep my weight stable, do it also because its just easy for me. I don't have to spend time or money to prepare or buy lunch or breakfast.