Your left eustachian tube is clogging and the pressure is lowering as your blood absorbs the oxygen. When you chew you sometimes let a little more air work it's way up.
It may be an allergy (hay?) or the remains of a recent cold (remember one?). It WILL clear up, but to hasten it take some steamy showers; sip plenty of hot tea and broths (steam room if you belong to a gym.). This loosens the clogging goo.
Pick up some Sudafed (or generic pseudoephedrine)- around 25 mg. and take one every morning til it clears.
If you can hold your nose, blow ever so gently til you POP the ear, it will help with the drainage (Remeain upright after you do this to help clear the gloop withe gravity.)
GENTLY is the operative word...you don't want earbones all over the barn

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