I don't have a darkroom but, if I understand well, your one has three openings while not in operation, but has no ventilation while in operation, i.e. while in its dark state? If that is the case, I would consider some form of ventilation for the dark state, which is when you are there breathing all the fumes.

As far as I understand, the air flow should pass above your trays and take the fumes away. You should not breathe just above the trays. Chemicals are not good for the photographer's health, even when he has not headache or any particular symptoms.