I get the ears plugged and a tone plays in my ear randomly.
If my head feels like it's under water, I learned it was a bunch of wax and I clean them with peroxide and an ear bulb. It helps a lot to keep that wax minimized.
My food sensitivity indicator is my left sinus cavity. When I eat something bad, it will throb inside and I'll know it's activating the squatters that live in there.