All night last night, i was kept awake because i kept smelling something that wasn't there. It -almost- smelled like my dog had piddled somewhere (chronic kidney disease :( ), but after sniffing just about every square foot of my apartment, I found nothing. It just comes and goes within a matter of seconds, even when I'm not at the house (ie at work, then grocery shopping).
Is there any kind of illness (flu, cold, etc) that may cause this? Or do I have a brain tumor? Or anything else?