Sleep Apnea Treatment

Sometimes I will wake up in the middle of the night gasping for air. Other times I will be lying in bed and have trouble breathing through my nose which will create pressure in my head. Also sometimes a part of my body will twitch usually my legs, The only thing that helps is if i sit up or stand up but when I lay down these symptoms will occur.
I am 6 ft. 135 lbs. If anything I am underweight.