I had a brain bleed but no anerysum or abnormalities found , so why did i have a bleed ? .

Subarachnoid bleed: Certain patient has artherosclerosis which is hardening of elastic artery which can be broke when sudden high pressure develops. No abnormalities can be seen until it perforate and bleed, most of time, high blood pressure related, as " subarachnoidal hemorrhage".

Depends on location: The location of the bleed may give you some hints as to the possible cause. Intracerebral bleeds tend to come from small weakening in the vessels inside the brain. Subarachnoid bleeds tend to come from aneurysms. Bleeds associated with a tangle of vessels may come from an arteriovenous malformation. There are also cavernous malformations which are sinusoidal dilations of vessels that can bleed.

"Brain bleed" is nonspecific, so these correlations might help: A subarachnoid hemorrhage is often due to aneurysm, or AVM. A subdural hematoma may be due to trauma. An intracerebral bleed can be associated with hypertension. There are other causes and sometimes combinations.