You can summarize in one or two sentences the why. It doesn’t need to be stated in any detail. Something like: I was dealing with a new mental health diagnosis, physical effects from a car accident, and deaths in the Immediate family.
Focus the rest on working with the psychiatrist on the correct medication, getting support, and all the things suggested by Linda. You need to explain how you will succeed and do things differently. They don’t need the details of what happened.