Your case seems to be of inter vertebral disc involvement, thus exerting pressure on nerves emanating out of spinal chord. Due to changes in said region and bending in vertebral column, blood vessels also get compressed somewhere and supply to brain is hampered with all the feelings you mentioned. While lying down, the column is straightened and supply of blood resumes. It may also raise BP temporarily because heart tries forcibly to send blood to brain. This is a natural mechanism. Medicine is not the proper answer. You should try to do physiotherapy, Yoga postures, deep breathing for ultimate benefit. Constipation is not directly connected. Try to eat light, lot of water and fibers, long walks etc will correct it. Hope it helps you.