A most definite yes, to that one, hungry,tired,in pain,or distracted by the ever on tv right next to me,and worse of all rushing moves, all effect standard of play.
Alertness and Consistency and Tactics Trainer

Agreed - a nice observation. I play at night after my wife and son are asleep. Unfortunately, I'm pretty sleepy at that point also, and my play is correspondingly sloppy. Coffee only marginally helps at that point :)

That doesn't bode too well for me. I'm in my twenties and my sluggish days are a STARK contrast with my alert days. My two big problems are poor diet and sleep. I wake up wondering what kind of day it will be for my chess and if I ate properly/effectively the day before. The good news is...I am trying to avoid playing my games if my tactics trainer work is crap. There is a clear correlation for me so it gives me a heads up when I'm not really sure how alert I am in actuality.
Nobody has mentioned if they see these sharp rises and falls with tactics trainer?

a picture says a thousand words....

I played over 23000 problems on the TT.
The tactics trainer is not a good gauge of your alertness.
Once you exhaust enough problems at a certain rating, it will select send you off to the closest rating, higher or lower. And the way the algorithm works, you will typically stick there. So, it may not be indicative of alertness.
The way the algorithm works you will stick in a cluster for a while. While typically I have been scoring in the 2200s. I had a hard time getting out of 1000 range, having cleared through all the problems from 1100-2100. I would solve 30 problems, accumulating small increments to my rating, then make one mistake, and lose 300 points off my rating. It's only after successfully solving EVERY problem below 2000 and slowing working up to the midpoint (around 1600), was I able to get a 2000+ rated problem, which I had to successfully solve. Once that happened, I was given about a 200 point boost to keep me in the higher cluster.

Exactly the same. I'm 30, but I blame it on playing late at night when I'm tired or early in the morning sometimes. I've gone below 1000 and then up to the brink of 2000 in a matter of days. Now I'm on the decline again! It doesn't help that the ratings of the problems often seem entirely random. I've struggled more with 1100 problems than with 1800 ones.
Same can be said of my games. On some days I feel attacking and inspired, other days I have no plans whatsoever other than not to lose!

If diet is bothering you so much you may have a medical condition like hypoglycemia. If I do not eat regularly, every three hours, I tend to feel it. If I have to skip a meal and go, say 8 hours, w/o food I will get a migraine and feel exhausted afterwards.
Many high level players say that physical condition (which would include diet) has a role in playing strength.

Karl. I haven't seen anything on this website for endgame play...on ICC they have a little trainer to give you endgame positions. Maybe they can make an endgame tactics trainer on here.
wesnerm. you're probably onto something with this cluster theory...though as headofwords mentions...I see almost no correlation of difficulty problems at 1100 and the problems at 1600.
Robert...that's exactly what happens to me...if I don't intake food regularly I feel extremely exhausted even if my last meal was abundant. I confess that I definitely don't drink enough water, either...so that's probably a lot to do with it.

The main reason my blitz rating is unimpressive is because I generally play between 10PM-5AM when I can't sleep. That & that blitz is not my strong suit.
I try to only use tactics trainer when I'm in a good frame of mind. Same thing with my coorespondence moves, that's the beautiful thing about coorespondence chess.

Maybe some of the new teaching videos cover endgames? And there is a category for endgames in the Computer Workout tool. I'm not diamond so I don't know what the chess mentor has but I would have thought it would cover at least basic endgame principles.
I'll check on what Chess Mentor has in that department and give you a full picture.
My daily activities/work can be achieved with very little mental effort. My health can be compromised along with a lack of sleep and I'm still quite capable. With chess, I've found it's not so.
If I'm lacking an iota of alertness, I can be sure it will be reflected in my games.
Where I first started noticing this stark difference is in the Tactics Trainer. On days I feel sharp and focused, my TT rating jumps by 300 pts and the puzzles feel like I'm eating candy. On days when I have neglected my diet or my sleep...it drops by about the same amount and puzzles look like squiggly lines on a paper. And my games end up being played the same way on these occasions.
Question: Has anyone else noticed this kind of contrast or fluctuation from day to day or are you pretty consistent?