Good you have surgery soon, and many members have had successful surgery with Dr Hackman!
@Isaiah_40_31 has pretty much covered everything, but here’s a link to our info about surgery, there’s even a suggested shopping list:
ES Information- Treatment: Surgery - Welcome / Newbies Guide to Eagle Syndrome - Living with Eagle
A constipation remedy might be helpful to get beforehand as some of the pain meds can bung you up!
Also worth being prepared for is that sometimes with surgery the facial nerve can get irritated, & it can make the side of your face feel weak or sometimes slightly paralysed, but this does improve with time so don’t panic if it happens to you.
The pain in the back of your head is quite common; it could be from tense muscles (because you’re in pain) which can irritate the occipital nerve, or sometimes if the internal jugular veins get compressed there can be veins at the back of your head which take over, & some members have found as these swell they can be painful. It does sound as if you could have some vascular ES symptoms, so it’s possible your IJVs are being compressed; it’s worth double checking with Dr Hackman that he’ll remove the styloids as close to the base of the skull as is safe to do so to remove any compression.
Best wishes for your surgery, if you’re up to it let us know how you are afterwards and praying that it goes well for you 
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