DATA, DATA, DATA, GIVE ME DATA!!!
Seriously, apply a tape measure in strategic places to quantify these changes.
There is gravitational rearrangement of fluids when you lie down but I have not come across reports of swollen arms before.
The pessimist in me might wonder if there is any mechanical obstruction to venous return from the upper limbs, which could be Seriously Bad News.
Do your arms and face look red or purple in the mornings?