No, I really don't believe your father has a multiple personality disorder. Those show up early in life, and are not overlooked by family. I'm sure sorry to hear you are now on "alert" to avoid his outbursts. Has your father had a thorough physical exam lately, say, in the past few months? If he was my dad, I'd be taking him to the doctor myself. There are an infinite number of reasons for older people's behavior to suddenly change. Many of those reasons are physical.
When all physical reasons are ruled out, sitting and conversing is the best route to understanding. And if that fails, you've done the best you can. And, as Stock Lady says, he might simply want his private space back. Don't try to read his mind. Do ask in the moment when you can. I hope this works out.