My wife has had myelograms, the last was for the entire spine.
One of the things they should have told you is that to avoid severe headache you should stay lying down for 24hrs, only getting up to eat & for potty breaks etc.
They neglected to tell me that and I have been up all day traveling by car, cooking, doing dishes and taking care of the dogs...wish they would have told me, I wouldn’t have had to deal with a headache all day. ;9