We carry a fair amount of dry ice in the cabin, for keeping things like ice cream frozen. Also if the galley chillers are on the blink.
On many passenger aircraft that I know, the air comes into the cabin, some of it is recirculated and some of it goes through the hold and then is exhausted without passing back into the cabin. On that basis, you are very unlikely to be asphyxiated by sublimed CO2 from the hold, any more than you are from that produced by the respiration of your fellow passengers.
There are certain requirements, one of which being you have to be careful when packing not to have livestock and dry ice in the same compartment, for obvious reasons. All that said, given that CO2 is not classified as toxic, and is in widespread use almost everywhere, I’d worry more about all the other things that could float around inside an aeroplane...