Or to be more precise .. the 'Black Dog' as Winston Churchill referred to it. I am personally not a sufferer of depression. My life is, by and large, excellent. I have a loving and caring family, a magnificent wife and kids; superb friends and a great job. Life is good.

However, every so often I have a day when for no discernable reason I feel below par, not at the races. Happens about every three or four months. Yesterday was such a day. My head felt 'scratchy' and thoughts were disconnected. Woke up this morning and the dog had moved on to gnaw at somebody else's bones. Ever had those days? Is it biochemical? Am I going mad?

Thoughts please ...

Well if it is every three or four months it can't be pmt related!
If you only get it one or two days at a time, it might be a food/drink intolerance/allergy that you are not aware of, that affects you that way rather than getting a rash, itching, swelling or migraine.
Next time you get it, think back to what you ate immediately before, or the day before yesterday, and see if there is a pattern. Then avoid the suspects and see if that does the trick.
Food intolerances can come on within minutes of the offending food or be delayed til next day, (speaking from experience) and can cause feelings of depression, fogginess and disconnection.
Or do you have any other physical condition you know of that could be affecting your head.

Black dog usually stays for longer, or doesn't really go away completely, and is not always related to how excellent your life is. Its more finding the ways to deal with it and keep it from taking over.
You changed your scary avatar anyway.