What Causes The Arms To Lose Their Circulation When Sleeping?

hi...for about 6months, i have noticed that my arms lose their circulaton when i sleep, i do sleep on my sides, always have but never had this problem before, what are some probable causes? i am female, 42, worked a "desk job" for 17 years and therefore am over weight, and i do take benicar 40/25 for hypertension, which is now controlled.