Sahasrara, which means 1000 petalled lotus, is generally considered to be the chakra of pure consciousness, within which there is neither object nor subject. When the female kundalini Shakti energy rises to this point, it unites with the male Shiva energy, and a state of liberating samadhi is attained (According to Wikipedia).
This is chakra seven or the crown chakra (Sahasrara) which relates to our self-knowledge, consciousness and pure awareness. It is our connection to the greater world beyond. When developed, this chakra brings us knowledge, wisdom, understanding and spiritual truths (Debbie Creagh).
This chakra relates to the physical functions of the Brain, Nervous, Spinal Cord, Nerve Fibers, Pituitary gland. Therefore, some of these symptoms can occur when this chakra is congested: Migraine, Brain Tumor, Amnesia, Coma, sensitivity to light/ Sound (Lee Wei-Dei).
(Citing Siam Reiki materials)