What Causes Pressure In Head Radiating To The Neck?

I have been experiencing tightness in my head that radiates down my neck. It comes and goes. Sometimes I feel a bit off -like a stuffy cottony headed feeling. Other times it feels like gravity is pushing down on me. I do have issues with sinus and did fly a week ago but don t have symptoms of a sinus infection. Did swim in ocean so not sure if I have water trapped in ear or what is going on exactly. Thanks for any advice you can provide