What is the worst mental illness?

How do you judge something like this? Naturally, many people would say psychotic disorders, like schizophrenia. The diagnostic hierarchy could lead you to think of a mood disorder - probably bipolar 1. It could be argued that the depression aspect of many mental illnesses cause ‘suicidality’, which would make that the worst. Then again, OCD makes life unbearable, so surely it’s a winner.

Mental illnesses like to bring along some friends, so you could be exposed to multiple illnesses. Would this make it easier or more difficult to determine the worst of the bunch?

Do we judge based on the quality of life or risk to a life? Are a schizophrenic sufferer and an anxiety sufferer on par, because they both suffer? Or does it depend on who is struggling the most?

Does this question have an answer or is it completely subjective?

For your reference, the following hierarchy demonstrates the 5 main categories of mental illnesses. Note that it’s not a hierarchy of severity, but an order of diagnosis.

1. Mood disorders

2. Psychotic disorders

3. Anxiety disorders

4. Personality disorders

5. Other disorders (e.g., ADHD, Eating disorders, Conversion disorders, Dissociative disorders, Sexual disorders)

The above points and questions are just triggers, the question being asked is the title - what is the worst mental illness?

Please be respectful.