After wicked hayfever attack, stuffy nose, sneezing, itchy eyes -- I noticed I couldn't taste food for a while. Why might that be? Thx.

Anosmia. The sense of smell is affected by congested nasal passage as molecules responsible for aroma cannot reach the olfactory epithelium located at the upper part of your nasal passage. In most cases, it is reversible in a young person with medical treatment of allergy.
The nose. The nose is responsible for much of tasting and smelling and thus obstruction of the passages can impair these functions. If the tasting function impairment persists even after the nasal passages have opened up, a sinus infection should be ruled out.