In my experience, it's better not to tell the employer, just say you need some time off for a medical reason. Tell your colleagues that you're taking time off for personal reasons. But this may be difficult if, as you say, your colleagues are friends. I switched to part time at one job for 10 weeks, in order to go to a day treatment program and didn't tell anyone why, and all my colleagues were worried that I had cancer and was getting chemo.


Good luck with it.