I always feel a cold coming on and start to dread what's ahead. Sales Sickness is similar; however, it's easier to spot in others.  You start explaining why it's been hard to close more deals. You begin to wonder if we should change things, offer new things, or discount more. You use phrases like "it's different here" or "this is that time of year" or "the economy is slow". 

If not cured, you'll end up losing and removing yourself or missing your targets by so much that we need to part ways. I do think there's a cure, but it's takes action.

You need to move -- both physically and mentally.  My car sales boss always told me when he was in a slump he get a hair cut and come to work early. I agree with him and I get lots of hair cuts. You need power ups. If it's a cold, you need to rest and maybe take vitamin C (no real cure is known but it's worth a try).  If it's Sales Sickness, you need to sharpen the saw as Steven Covey is famous for saying. Study your company, what you offer, and how's it's done. Call a rep that's having a better day and ask questions. Don't spread your disease. Ask questions to learn. Don't confide and complain and talk about how tough it is. No one wants to hear and besides your Mom, no one really cares.

And physically, go for a long walk, get up 30 min earlier, go to bed an hour sooner, play with the kids -- just do something to get the blood pumping. Changing the body will quickly change the mind. 

Send me note and I'll talk with you about a plan to correct. The key is to act sooner. Watch for signals. It always start with a poor attitude and not taking ownership for performance. The refs aren't fair but it's part of the game. Learn to play through it.Good luck!