I have restless legs too. Bothers me at night and sometimes in the car or plane. Best thing for me is to get out of bed and streeeeettttch them - lunges, squats, etc, fronts and backs and sides of thighs and hips and buttocks. Obviously not so easy in a plane...
I've looked for connections to caffeine, sugar, not enough exercise, too much exercise, pregnant, not, full bladder... but not consistent. It does seem associated with sitting or lying on the buttocks. if you weren't pregnant, you could try rolling over...
Other remedies I have heard:
1) Eat a banana (for the potassium).
2) Wear leggings to bed - snug fitting the whole leg
3) Foot massage
4) Elevate head or foot of bed (not sure which) on a brick
5) Take a prescription medicine that has other side effects -- you'd have to be really desperate, seems the fix is worse the problem. And don't even consider that while pregnant or breastfeeding.