Can't say until you explain how you feel different--for all I know it could be blocked sinuses.
A touch of depression, or maybe you're just tired out?
you just need to get back to what makes you feel better
What you need is a good mental health day. <br />
Or as Brokenantenna said, go get it checked out if it's really starting to worry you.
I think you need to get drunk, c'mon over and we'll pop a cork!