Unexpected Nose Bleed

I had constant nose bleeds as a child - it turned out to be a sinus problem. To this day I have occasional nose bleeds because my sinuses are very sensitive - very dry air, pollen, smoke , dust, there we go *ugh. I HATE IT. Luckily it is not often, maybe once every 3 mos or so.
Regarding Cialis - it actually causes vasodilation and lowers blood pressure so it would be an unlikely culprit, but ask your doctor anyway.
I would not worry too much < 3 unless it becomes often and in that case you might wish to visit ENT doctor to check if you have an infection or inflammation of sinus membranes.

The cause of my mother's nosebleeds was extremely serious. I would consult a physician sooner rather than later.

One cause (for me, but usually n the winter) is the fragile membranes in the nose get irritated. Due to dry air in particular but just blowing my nose can start the bleed and there is a lot of blood with these bleeds sometimes.
Hopefully it isn't more serious than that.

I am sure you checked that your blood pressure has not risen too high.

I would say it is a nose bleed and to not get to excited about it unless it is reoccurring as in many days in a row and in that case, go see an ENT. I used to have them as a kid all the time until they cauterized a vein in my nostril.

I just got back from my PCP and they found nothing in my nose that suggested anything other than a nose bleed. Since I was in a department store they think something in that store irritated my nasal lining enough to cause the bleed. My BP was fine etc. So I'm a worry wart, what else is new.

I am so glad you checked it ! Why worry about some extra thing when one has enough on his/her plate already ;). I am sure that is was an isolated event and that you will not have to deal with this sensitivity long term, like I do. I am "human canary bird" for many things *eyeroll lol