Making the world better, one answer at a time. Technically a mentally health person is a person who is able to function on a high level. For example, is able to look after themselves on a day-to-day basis.However, mentally healthy people can still get mental diseases such as depression, where they can function well.aking the world better, one answer at a time. Technically a mentally health person is a person who is able to function on a high level. For example, is able to look after themselves on a day-to-day basis.