Here are some mental health topics:
What causes depression?
What is causing anxiety to become the most common mental illness in young adults?
What effect does having a family member experiencing depression (or choose another mental illness) have on a family?
What effect does having a co-worker with a mental illness (choose a particular one) have in a workplace?
You might also want to look at my article describing how to write this kind of essay effectively: https://owlcation.com/academia/How-to-Write-a-Spec...