Most don't have a problem, unless claustrophobic. The first day was the most difficult, but after that no problems, and just watched movies, so the time went by..2hrs. I did did hear of people with cataracts, near sightedness may worsen in some cases, and actually may improve far sightedness temporarily. I guess there are some underlying issues to be considered by the doctor there, and you are closely monitored while in the tube. I needed my glucose level, bp, checked before each dive by the nurse. If my blood sugar level was low, even 130, they made me wait, and drink juice, eat cookies since the HBO may lower it, and usully did when they rechecked afterwards. A few times I had to drink something after to get my sugar up before letting me leave. Some get tired, I did, or have ear problems if having a sinus problem or other esr issues, which may cancel a treatment, but your ears should equalize on thier own or by dry swallowing. Good luck.