I would think (as a lay person) either a psychiatric disorder (bipolar disorder?) or some form of dementia. My friend's husband started acting like this and I believe it was Lewy Body dementia. https://www.mayoclinic.org/diseases-conditions/lewy-body-dementia/symptoms-causes/syc-20352025 See the section on diagnosis.

Clearly he needs to see a doctor, probably a neurologist or psychiatrist. In my area there is an "adult" psychiatric geriatric unit that does diagnosis.

The problem is, how do you get him there? I would suggest your mother discuss this with his PCP. Without his permission, she can still write on the portal or write a letter even if the doc cannot respond.

If the situation becomes dangerous, the police and ambulance can take him to a hospital to be diagnosed.

This situation sounds concerning for your mother. Is there a senior care service where she can call and get advice? Our local senior care service also runs support groups where spouses suffering from situations like this can get advice- or their kids, like you.