The road climbs from 910 m at Dharchula to about 4,570 m, and there is no hospital anywhere above Dharchula. The administration screens every traveller twice, at Dharchula and at Gunji. Fitness is not protection against altitude sickness, so please speak to your own doctor.
The road takes you from 910 m at Dharchula to about 4,570 m at Jyolingkong. The figures in between come from Ministry of External Affairs yatra itineraries: Budhi at 2,710 m, Gunji at 3,160 m, and Nabhidhang, the Om Parvat viewpoint, at 4,260 m.
Read those numbers alongside one more fact, which matters more than any of them. There is no hospital anywhere above Dharchula. Medical cover on the entire stretch above the town rests on the Indo-Tibetan Border Police and the Army, and evacuation from high ground is not something anybody can promise you in advance. Dharchula is the last town with a hospital, and it sits at 910 m, near the bottom of the climb.
That is why the administration screens travellers twice, at Dharchula and again at Gunji, and why a screening on the ground can end a trip that a certificate from home had cleared. It is not bureaucracy. It is the only intervention available on a road where the nearest ward is a day behind you.
Sleeping altitude is what your body responds to, more than the highest point you touch during the day. From Gunji onward you are sleeping above 3,000 m, and acclimatisation means gaining that height slowly enough that your body keeps up. A four-day permit does not leave much room to go slowly, which is a real constraint on how this journey can be built rather than a detail.
Fitness is not protection. Altitude sickness is unpredictable and affects people who walk every day as readily as people who do not. Please speak to your own doctor about your own health, particularly about blood pressure, heart conditions, diabetes, asthma and any breathing difficulty. We are not qualified to clear anybody, and we will not pretend to be.