I experience extreme dizziness and disorientation upon standing after I sit/lay down for more then 10 min. Is that caused from previous concussions?

Tizanidine. is a centrally acting Alpha 2 agonist that is known to cause orthostatic hypotention even in low doses (2 mg). I rarely use it in individuals who are not wheel chair bound with MS. You need to have your blood pressure and pulse checked in the upright and supine position with and without this medication. Ketamine is a hallucinogenic anesthetic popular in Rave Culture. See a neurologist.