'Hypoxia' is the condition when the body does not get sufficient oxygen, and 'Hypercapnia' is a condition in which elevated levels of carbon dioxide (which you normally breath out) in the blood causes dizziness, shortness of breath, headaches and in some cases hyperventilation, seizures and even death.
There is an arising incidence of reported cases of 'Hypercapnia' among workers who are using the N95 masks associated with their employment in order to reduce the risk of COVID-19 infection. It is not yet know if this arises from cases of improperly using the N95 masks, or perhaps using some of the N95 masks that were 'bootlegged' and did not actually meet strict standards, or if this is simply arising from the extended wearing of the N95 masks among those reporting the incidents. There are other possibilities such as 'extended use of the mask' beyond the intended life expectancy without proper cleaning. Another factor could be contributory preexisting respiratory illnesses. At present too many differentiating factors exist to clearly identify all of the contributors that should be included in these claims versus those that should be ruled out.
Researchers currently believe that N95 masks may actually reduce the current intake of oxygen when breathing room air via the mask by as much as 20%, this combined with the increased carbon dioxide retention could be producing a combined effect of some extent of 'hypoxia' and 'hypercapnia' depending exactly upon how each individual is wearing the mask. But that is also part of the problem. No two individuals do in fact wear these masks in exactly the same way even though they are instructed to do so.
So, for now there is no concrete evidence that the N95 mask is exact cause even though the Center for Disease Control admits that their studies show that N95 masks do trap carbon dioxide, but they say not in dangerous amounts.
This too will be another issue that the employees who are filing claims will ultimately have adjudicated in the Workers' Compensation Courts. There will be countless attorneys involved and industrial engineering experts, along with this kind of specialist and that kind that will all give various 'expert witness' testimony and in the long run each State will determine what they feel is the liability they expect the various Workers' Compensation Insurance Carriers to be responsible for. Those carriers will then turn around and file litigation against 3rd parties they believe who are 'contributory' in an attempt to draw them in to quagmire and help pay the costs of the claims that will paid.
COVID-19 will turn out to be far more than 'disease claims', almost anything to do with it will likely in one way or another find it's way into some 'court'... if not Workers' Compensation Court, then Civil Court. And why, because that's the 'American Way of Life.'