When do we need a change? and what should we change?

Today is another day (in a set of three) where the motivation is low. Is it because I have had a few days break- and the adrenalin from the earlier deadlines has settled down, and with the few days break it has totally disappeared. In any case it is a bit hard to be motivated to start the next job. It could be the nature of the work- research always need a lot of discipline to start a project- and with lots of deadlines it works well, but the lull can be such a motivation killer. Or it could be that the work rhythm changed- working constantly was fine, but then the break came in and destroyed it. So if I change something - what should it be the? the way I work, or what I work with. It is also funny since I am actually good at what I do- but is it the competitiveness in me that makes me good. And would I be good somewhere else- is it that fear that I may not be good that stops me taking the risk and changing.