I certainly hope you can find some answers soon. This would worry any concerned parent.
You mention that he goes in and out of these "seasons". Have you noticed any particular events that cause him to start and stop feeling this way?
Interesting that he's a nurse yet refuses to see a doctor. Is it possible he had some traumatic event that causes him to question the profession? PTSD can take strange forms sometimes.
He mentions being exhausted -- is it possible he has a sleep disorder?
Does he ever express irrational anger? Or is he detached and indifferent?
Does he have a spiritual life? Belong to a church or other group? Have interests in any particular spirituality?
So many questions, yet only a qualified professional can help with answers. Hopefully, you'll find some soon. Best of luck to him, to you, and your families.
Thanks Scott for your response and thought-provoking questions that are making me see the bigger picture of this problem. The first time i saw him depressed was in 2019 when he split from his GF of 3 years and later he stopped working as a nurse from a reputable hospital. He was depressed for about 6 months and one morning he woke up, applied for jobs and started working again. Again since the start of this year, 2024 has been depressed so badly that he sleeps most of the time. This time round I have particular reason why he is upset, apart from the fact that immigration have taken 2 years since his wedding to grant her a visa to join him. Prior to start of the year, he has no sleeping issues. I doubt if he has any sleep disorders. No anger issues. Used to be very pleasant and warm but currently he is very aloof and detached. Prefers to keep off in his bedroom and not join us in the leaving room.
Used to be very active in the local SDA church. Very church oriented but now has lost all interest and does not attend since he started being depressed.
This is a very though time for and rest of the family as am personally dealing with other medical issues (diabetes, high blood pressure, CKD and lately have a blood disorder that is being investigated)