light headed, almost passing out, strange dusty smell?

I am getting nausea, very light headed, almost to the point of passing out or stumbling when walking. Also have a very strange smell which nobody else can smell, its almost like a burning or dusty smell. It doesn't happen all the time but when it does it can last up to 3 days. It has no relation it seems to my diet or anything, not a heavy drinker. i do smoke though. it has been going on now about 6 months. Please help.