Thank you for this post. It highlights the gulf between two types of joy- absence:
a) Some irrational inexplicable misery despite having nothing to worry about, which therefore must be a mental disorder needing treatment
b) Some inevitable non-enjoyment of an unalterable external situation.
Normal human lives will contain grief and problems, but during our current lifetimes, in the affluent West, this can be 'pathologised' and 'medicalised' for profit.
There's no need for O.P. to explain the unalterable external situation. There will be millions of people with their own versions. It seems worryingly easy to hand all of them a label of mental illness, and a bottle of pills, or even send them to talk to someone for a few sessions of 'mental illness talking therapy'.
It isn't mentally ill, to have a normal response to a situation.
However, the placebo effect is brilliant, as others say, you don't even need to believe in Reiki or something else: Whatever works, works. It probably is partly at least the Attention.
Lately, experiments have shown that results from some prescription drugs are no different than from bottles of pills plainly marked 'Placebo', and with the participants clearly informed there is no active ingredient.
(Chronic pain and even need for surgery can be 'cured', which is probably the explanation for homeopathy and other 'alternative' methods. They must all be far preferable to drugs, because they don't have side effects. )