Hi.. On lying down, the blood flow to the brain and the scalp increases which could be the cause for the pulsations.. The same implies when one is tensed and stressed... Change of posture can cause giddiness either because of postural drop in BP or due to vestibular dysfunctions in the ear.. You may have to check this from your doctor.. And as far as the pulsations, if there is no headache, it would not be of concern..