My boyfriend has been in a hurry at times and entered to perform deep intercourse before I am fully aroused.
I am post menopausal; but after a deep penetration there has periodically been bleeding with some clots.
The bleeding stops in due course. The sensation I experience is as if I am having menstruation.
A gynecologist has cleared me as perfectly healthy.

Is this the lining of the uterus which has been disturbed and is separating from the uterine wall w/accompanying bleeding?

Although I know that I need more arousal before intercourse, is there any downside to this occasional bleeding?
We are a monogamous couple.

Is it period blood? Or is it bright red blood? If you're Gynecologist has cleared you than you should be fine, but this is concerning.

Lube. If you're not full aroused then use lube. You can buy it in the store or you can buy it online if you're too embarrassed. If the problem continues I would get a second opinion.