Can i cause an aneurysm by straining during a bowel movement? i sometimes get a headache afterward.

Maybe. Ask one's Dr.: An aneurysm is a ballooning of an artery at a place where there is a weakness in the artery. Some people are more likely to form aneurysms, such as people with genetically weaker connective tissue. Aneurysms usually take decades to show up, so middle aged and older adults are the people at risk. Arteries have pain sensation so that straining on poop can cause a headache even without an aneurysm.