Sometimes when i lay down i can feel a slight pulse in the back of my head when i'm resting it on a pillow. is a noticeable pulse in the back of the head a possible symptom of a brain aneurysm?

Unlikely: With thin people, it is often possible to see or feel pulsation in the head or neck when at rest. This is normal. You would very likely never feel a brain aneurysm before it ruptured. I believe if there is a family history of brain aneurysms, screening may be indicated. Here is a link for more info: https://www.bafound.org/about-brain-aneurysms/diagnosis/early-detection-and-screening/