I left the wardrobe door open while I slept in my bedroom...Can the smell of naphtalene harm me or my brain?

Possible poisoning! When you smell mothballs, you are inhaling naphthalene. People have developed headaches, nausea, dizziness, &/or vomiting after they're exposed to naphthalene vapors. Hemolytic anemia & cancer may occur from naphthalene poisoning. If you suspect poisoning call the National Poison hotline at 1-800-222-1222 or 911 in an emergency. Go online to https://www.aapcc.org/ for more guidance. .
No, but it's the... It's the amount of naphthalene that gets into a person's body that can be toxic. The smell isn't necessarily the problem. Some people have very sensitive noses and can smell the mothballs' naphthalene the moment they set foot into a house they are visiting. It is hard to figure out how much naphthalene in the air is too much, if just going by smell. Better to use other insect repellents.