Numbness while sleeping

I'll be 26 weeks with my di/di boys on Tuesday and for the last few days I've noticed after I sleep for more than 2 hrs my arm and/or hand that I was laying on will be asleep!!  It's so annoying cause no matter how tired I am I have to wake up whatever fell asleep and then try and fall back to sleep. Just wondering if any other moms have experienced this. Thanks!!