Also, if I smell something, I can smell it again after a little bit even when I am not exposed to it.
The smells vary from burning to perfume. For example, I was just thinking about cake and a couple seconds later I tasted cake in the back of my mouth and sort of smelled it. They usually last 1 second. I had them a year ago and they went away but recently came back a couple days ago. I also have a very foul taste in my mouth. My head feels very foggy and i had a headache last night. I also get a tingling and weird sensation when the smells occur. I have been very stressed out since the smells started again.
I would recommend ruling out a medical cause first. Can you describe the smell/taste? How long has it been going on?