Some people worry that plants in the bedroom will cause carbon dioxide (CO2) poisoning, but this is an urban myth. It’s true that when you turn off the light, the plant no longer has a source of energy, and so photosynthesis stops. This means that it no longer takes in CO2.
Meanwhile, in the dark, the plant continues to respire – a process which releases CO2 (the exact quantity of which depends on the size of your plant and its species). However, any plant small enough to fit in your bedroom produces far less carbon dioxide than a sleeping human, and is perfectly safe to share a room with.