I had another thought: if he has allergies, his ears may be stuffed up and this could cause vestibular syndrome. This condition usually starts in the ears with an infection or other disturbance in the vestibular system, which regulates balance and equilibrium, so if his ears are stuffed or he should have an ear infection, plus, this could make him feel dizzy, he may feel too off balance/unsure to jump.
In addition, if he's sneezing and his eyes are watering, as long as the discharge is not greenish/yellowish, indicating bacterial infection which would need to be treated by an antibiotic, for the moment, you can give him an antihistamine to help.
A good one is Chlor-trimeton, available over the counter, and you can give 1/4 of a 4mg tablet every 12 hours, and see if this helps. A side effect can be sleepiness. Make sure to use ONLY an antihistamine, not a 'multi-symptom' antihistamine product also containing a decongestant like psuedoephedrine or any decongestant, a pain reliever like acetaminophen (Tylenol) or Advil (Ibuprofen), etc., as these medications are very dangerous to cats and they can't tolerate them. Here is more information about Chlor-Trimeton:
You can also run a humidifier in the rooms he occupies most, to help with congestion.
You can bring him to be checked out at no cost to you, to a VCA animal clinic, which provides a downloadable coupon for the first visit for new patients, here:
VCA has offices nationwide, so helpfully, there is one near you.
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