A man's concern, even his despair, over the worthwhileness of life is an existential distress but by no means a mental disease. It may well be that interpreting the first in terms of the latter motivates a doctor to bury his patient's existential despair under a heap of tranquilizing drugs. It is his task, rather , to pilot the patient through his existential crises of growth and development.
Viktor E. Frankl, Man's Search for Meaning
philosophy, psychology