Yes it is a possibility but it is something a doctor can decide, the first step would be for him to see the family doctor.
Does your Father feel aware of his moods? Does he talk about wanting help? A lot of the time when high we are unable to see that we are ill or acting differently, but when depressed we feel very desperate indeed.
What strikes me about what you have said is there is such a marked change in mood, that is what defines Bipolar, it is literally from one pole to another, the two extremes are very different. The irritability is also a sign.
It does sound like he is suffering, whatever it is it is not nice and requires treatment just like any other medical illness..
Good luck!
Im not a doctor but it sounds like a possibility.Is he willing to seek help?