Unconsciousness or a seizure. The increasing pressure of an aneurysm on the surrounding brain and the nerves thereof can cause a seizure, which is severely disorganized brain activity (generally electrical in nature). A seizure is unmistakable and can cause convulsive and exceedingly odd actions on the part of the individual, as brain cells are randomly excited or inhibited as a result of the seizure. While an aneurysm does cause the seizures, it can also equally well cause complete unconsciousness.