I found this on the Web. Evidently the headache occurance can be caused by both, skill of the anesthesiologist and patient individuality. It is caused by a puncture in the dura.
"What can be done about the
headache?
The hole in the dura will usually mend itself in a
number of weeks but it can take longer.
Lying flat and taking simple pain relieving drugs
(such as paracetamol and ibuprofen) may help.
You should drink plenty of fluid (some
people find tea, coffee or cola especially
helpful) and avoid lifting and straining.
A severe post dural puncture headache will
often need to be treated by an ‘epidural
blood patch’.
Being given a blood patch is like having an
epidural and takes about half an hour.
The anaesthetist will take your blood and inject
it near the hole in the dura where it will clot,
forming the blood patch. This will tend to plug
the hole.
A blood patch will usually cure the headache
within 24 hours. After this period, if you still
have a headache, it may be worth repeating the
blood patch once more. It is very rare to need
more than two blood patches. Your
anaesthetist will discuss this with you.
After a blood patch, we recommend that you
lie flat in bed for 4 hours and do not lift
anything heavy for at least two days."