What Causes Extreme Mood Swings In A Person Having Diabetes, Hypertension And High Cholesterol?

For the last several months my father, soon to be 65, has been having fits of rage at work, has been combative with individuals, cursing profusely and having mood swings, all while at work, at home no disturbences. In April he had a stroke, but the symptoms have been going on for some time prior. His 2 older brothers had the same symptoms over time and eventually both had to be put in a nursing home or at home care. They were never diagnosed with Alzheimers or Dementia though tested for both. His family does not have a history of mental illness. I will list his current medical conditions, past medical and his family history. He has type 2 diabetes, hypertension and high cholesterol. In 2004 he suffered a mild heart attack and had 2 stints, in 2005 he contracted a lung problem do to the exposure to bird feces (the name escapes me), he has had a stroke recently. His father died from colon cancer, mother had a stroke and type 2 diabetes as well as a thyroid disorder. His 1 sister died from colon cancer, 1 sister still living has type 2 diabetes, 3 brothers all died from heart related illnesses, 1 had been medicated for thyroid disease earlier in life but was taken off the medication. Does anyone have any ideas what could be ailing my father? I suspect Thyroid Mania; we hope to get him tested as soon as possible.