The Veterans Administration (VA) has had me see both over the years. First time was in 1996, when they gave me a "provisional diagnosis" of ALS (Lou Gehrig's disease). Always terminal and not a pretty way to go, they assumed I'd need psychological support. Not me.
Unimpressed, I told them I'd wait until the diagnosis was confirmed, which depended upon the development of more symptoms over time. They never did, and 16 years later I'm told they never will at this point, a misdiagnosis.
Instead, 3 years later the VA diagnosed me with epilepsy, and that one has stuck. And once again the VA had me seen by mental health people, since depression is common with the condition, running about 60%. I got put on every kind of anti-depressant as a standard procedure, trying one after another as each one had side effects that were unacceptable to me.
I saw no improvement in me, nor did others who knew me. Instead, I became an emotional zombie, and a sexually impotent one at that. I told the psychiatrists that I couldn't think of a better way to MAKE a man depressed than to make him impotent.
And the reason there were no improvements was because there was nothing wrong with me in the first place. DUH! I dropped all their meds, except the anti-convulsants for the epilepsy, and I've never been better.
I believe depression can be situational, or medical. Situational when your mother has terminal cancer, medical when you have some condition that produces it. Situational when you learn you have cancer yourself, one that killed your own father, and it's not a misdiagnosis. So that I jumped the rails myself for a few months, both depressed and having a bit of panic, before pulling myself back together. I took no drugs for it.
Situational depression can go away by itself when the cause of it is resolved. Medical depression may require more long-term treatment, like the VA thought my permanent epilepsy would need.
I will not contradict what the OP's psychiatrist has prescribed for him. But I would suggest that he discuss with the doctor the option of weaning him off any drugs, if he remains on them today. If, or when, the situational issue of his mother's terminal cancer is past, the need for Prozac-like support may diminish until it can be removed. A decision for the doctor, but a question which the patient should ask.