What Causes Headache On Getting Up After Sex Or Massage?

one of my friends and i were talking and she stated that any time she is lying down whether a massage or during intercourse and she goes to get up she gets a severe headache that last a few moments that feels like her head is going to explode. She has had this for years following the birth of her children. What can cause this and is there any remedy that will make this embarassing issue better for her