I'd say it depends on the brand you take; all hay fever tablets contain one of two key ingredients. In the height of the summer I do feel the difference if I take Clarityn - like running on sand - I definitely feel some fatigue. Maybe try different brands as ok (ish) when I went back to Piriton.
At the end of the day they are non prescription drugs so will have some impact - you could always try other options such as eye drops and vaseline round the nose?
Hope you can treat yourself to a new pair of skinny jeans as one of your rewards for Paris...... how sore must you have been to have feet so swollen you had to cut yourself out - or is that more of a status of how tight your jeans really are ! ha ha .