Sundowning usually happens during evening hours... I would actually consult a sleep clinic, to be honest. Before a psychiatrist.

There are some uncommon but not super rare sleep syndromes that can cause individuals to behave very bizarrely at night... in various ways... the reaction the medication and the original breakdown may or may not be coincidental. If he is having problems with depression, yes he should see someone about that as well.

However, if these issues are almost entirely occurring at night, he is likely having some serious circadian issues as well which can have a drastic effect on mood. It makes sense to address that before the mood issues if at all possible. It is possible there could be some improvement in mood if there are any sleep problems present to address.

Though it makes the MOST sense to triage- if he is in a crisis situation, mood issue first.

that is what I would do anyway.
I'm not a health professional ny any means.