Being bored can make the tiredness worse. Likewise, frustration can affect concentration. I was like this in my last job: worn out, poor sleep, very poor concentration, BUT..new job (same field but nicer place) brought a surge of interest and motivation. I am still tired but it's a happier tired and I'm catching up on sleep. One other thing...I always found that irregular hours plays havoc with the digestion until I discovered the 'little and often' approach. When I know I am in for unpredictable work / rest pattern, I go armed with peanut butter and marmite sandwiches or peanut butter and banana sandwiches. You probably hate both but make your own version of high nutrition, portable, cold food that you can have every few hours on the move. Only takes 5 minutes to prepare with minimal shopping and is loads cheaper than commercial fast food. Drink plenty and I'm sure you'll find your energy levels stabilise and concentration will improve. Finally, don't forget the old black dog you are occasionally plagued by is a b*gger for slowing up the thinking process. I am sure you have all your previous faculties, undiminished - you're just tired, a bit undernourished and maybe still a bit low in mood?