Variations in how your system sounds?

Apologies if this has been covered elsewhere.
My system sounds consistently good to my ears for the majority of listening sessions but every now and again (say 1 in 20) it sounds slightly 'off' -- not its usual self. It is a very small difference but i do hear it. I would describe it as a slight lack of focus and dynamics. This has happened through many changes of all components.
Is it my mood, or hearing variation? Do i need to filter my power? Do you have similar experiences?
'I DO NOT can playing a digital track on a system demagnetize it? This will be added to the 12,416 things I don't understand, unless somebody can explain it to me.'

Does the term 'MONEY' ring a bell? Actually the disc works on the same principle as 'hospital grade' outlets.
Rok2id: The disc was free, so along with your inability to explain how a disc can demagnetize my system you rendered your entire response irrellevant.

I replaced the cheap $1 outlet for my system with a PS Audio Power Port. That's something I DO understand.
'Wolf_garcia: The disc was free'

And just how was I supposed to know that? :)
"I would describe it as a slight lack of focus and dynamics.* This has happened through many changes of all components."

I've had similar issue in the past. Check your incoming ac voltage, usually a drop would result as such*. Whereas, an increase could have it sounding too controlled and pinched. Get a power conditioner incorporating stabilizer, or, if separately, a good stabilizer along with your conditioner. I've learnt it's not so much about ac quality in this case, but more likely the irregularities of it being the culprit.
You didn't mention if the problem shows up with all sources , that may tell you allot . I used to have an issue with music sounding better in the evening , I upgraded to a high end conditioner and that problem was solved .