Older person's mental health

[Designerenvy]

Just looking for a little advice or see if any one has had similar experience.
My Dad has become very depressed and anxious, quite suddenly since Nov.
It's getting progressively worse . The GP has been helping and had prescribed some meds but , if anything, he's getting worse.
He's very agitated, restless, no interest in anything or anyone, mood Is very low and morbid. Talking a lot about death.
His gp has had him admitted for tests , just to rule out anything medical. Everything looks good so far , so it Does look like a mental health issue.
Has anyone had an older relative develop symptoms like these out of the blue.
If so, did they overcome it and move on ?
What helped ?
Thank you.

These questions may help me understand if you would like some thoughts. If not, think about them anyway.
How old is dad?
Does he live alone?
Has he been anxious about 'things' or money going missing?
Has he had a knock on the head recently?
Did he have trauma in his early life, or since?
What is his sleep like?
Is he losing weight?
Has anyone 'unusual' outside of the family been calling or visiting him?
Is he drinking water regularly. (or anything else)
Is he lonely?
Is it coming up to any particular anniversary of loss etc?

He's 79, living with DM.
Lost about 2 stone in 2 months without trying.
He has type 2 diabetes.
Not sleeping the last 2 months.
No injuries lately.
Has been stressed about DM for the last year after she had a long illness. She's good now and practically back to full health and I'm wondering if this is in response to the past year ?
No unusual visitors .
No particular anniversary.
Dischraged from hospital, they feel he's fine medically but have changed around his medications for anxiety. He has slept better the last 2 night with new meds .
Thanks for reply.