If the level entering the body through the lungs is too high, the dead bacteria, viruses, and oxidized toxic poisons leaving the body will plug up the channels of elimination making the chest feel tight, or perhaps making the nasal passages and mucous membranes swell up slightly. Same for ozone. You are breathing it right now. It is part of nature. Extreme levels of ozone make you feel you are suffocating, because the lungs swell to protect the internal organs by not transferring the gasses inside.
Conscious people turn the machine down or off long before that level is reached.
Normal people who accidentally breathe extreme levels of ozone recover in a short time without permanent damage in all but the most severe cases. Any one of them is acceptable to me. If you see nitrous compounds as something to be avoided, one manufacturer states that their line of electronically specialized ozone air purifiers produces no nitric compounds. All the other manufacturers have been selling products for years without anyone ever complaining about harmful effects - as long as their products were used correctly. That, and deliberate disinformation articles knocking our friend ozone is the only real reason why you hear warnings about nitric compounds.