How long has he been known to be BP and has he been diagnosed BP. Can you ask him or does he have a spouse / relative or doctor you could talk to?
Meds can work very well, but if they are changed, miss-prescribed, taken incorrectly or with another medication (even some over the counter ones) or simply stopped...A perfectly functioning person can behave as you mentioned.
I hope you are able to find some answers and get him some help.