What is my risk of brain aneurysm based on my age? 26/f. blood pressure always normal. throbbing in head for few seconds when i stand up/bend over. feels like a lot of blood rushing to my head?

Unknown risk: Unfortunately there might be other things we would need to know that could affect your risk such as personal history do a previous aneurysm , family history of brain aneurysm, congenital anomalies or syndromes , other aspects of your medical history. The good news is that you symptoms can likely have multiple alternate explanations so see you doctor ASAP to discuss further.

No different: Even with Hashimoto's thyroiditis your risk of having a cerebral aneurysm with those symptoms is the same as somebody with no symptoms whatsoever. These are not the symptoms of a brain aneurysm, ruptured or intact. More likely to have sinus issues. Once in a blue moon a colloid cyst of the third ventricle or low CSF pressure will produce this picture.

Brain disorder: Aneurysms are relatively uncommon, and you have a very low incidence of of this being present or a cause of your symptoms. But if focused on addressing this, imaging can provide peace of mind, and simple preventative interventions should be of value.