What Causes Frequent Nose Bleeds?

My husband (aged 59) has been having nose bleeds for some days now. He has had them during the day but also has woken up with them in the night. They are quite bad but controllable lasting 5 mins or so. he has had up to 4 a day/night.
I have taken his blood pressure with a home monitor on a couple of these occasions as he is a hypertensive on several medications including captopril, amlodipidine, irbesartan, pantoprazole and bisoprolol. His bp has been high at 188/108 on these occasions but on resting for 15min has returned to 140/80. He has no headache but his short term memory loss has become very noticeable in the last week.
Do you think this is just a weak blood vessel that needs attention, a side effect of his medication or there is another underlying cause?