Had severe sinus trouble once when on a solo CPL nav. Went and got it checked up with an aviation doctor who then sent me off to have a CAT scan. It showed that my sinus opening were quite small. Apparently this is a fairly common problem but is generally only a problem with flight crew and divers. I then had an operation to correct the problem and now it all seems to be working fine (however the whole process left me on the ground for over 2 months and wasn’t entirely pleasant).
Bing
The best nasal spray I’ve come across is Beconase. Doesn’t make you drowsy etc. but for memory is only available on prescription.
Have a good one, Dave.
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Flying is easy - just throw yourself at the ground and miss.