Every Night I Have Been Having The Same Issue. I

Every night I have been having the same issue. I lie down on my back and play games on my phone (so my hands are slightly elevated) before I go to sleep. It never fails that my left arm/hand begins to fall asleep so I have to keep it next to my body so it wont tingle. This started maybe 2 weeks ago.
I also have been getting dizzy when I stand up. I went to the doctor for the latter and he said I am probably dehydrated. I drink a lot and still have that problem every sometimes more than other days.
Should I be concerned?