I'll be going in May, coming from San Francisco. The Oxalis website recommends arriving to Vietnam a few days before the 5N6D cave tour to acclimate to the weather. But due to logistics, I'm only able to arrive in Vietnam the day before the tour starts, and to the specific city morning of. I'm flying business class to Vietnam, so there will be flat beds on the plane.
For those of you who have done the Son Doong tour, how necessary do you think rest days beforehand are? (I am a fairly active person in general.) Thanks in advance for any input.