I've always suffered from blocked sinuses and find that swimming makes a huge amount of difference - by which I mean "with-your-head-under-water-and-breathing-out-your-nose" swimming. Undoubtedly off-putting for everyone else, but the balanced pressure between your skull and the water helps to 'blast everything out'....

If I can get a good session in soon after/the morning after a flight then I'm a lot better off.