Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for severe shortness of breath, chest pain, a seizure, fainting, new confusion, or sudden weakness.
These are emergency symptoms rather than issues to wait to discuss at a routine appointment.
Contact the hyperbaric team promptly for persistent ear or sinus pain, reduced hearing, ear drainage, new blurred vision, repeated low blood glucose, fever, congestion, or worsening wound symptoms.
The article also says
Mild tiredness or brief ear fullness can usually be mentioned at your next session if it is improving.
Tell staff before treatment if you are having trouble clearing your ears.
Every sign above is quoted from the sofidex article on Hyperbaric oxygen therapy. If you are not sure, err upward — it is always reasonable to be checked.