Procrastination or lack of motivation?

Is a lack of motivation and procrastination the same thing? I've had one or the other all through the week. As I've posted, the book I'm working on, or trying to work on, can in no way be described as 'light' and maybe that's it? Maybe it also has to do with the email I received from an agent last week who said my work was intense, claustorphobic and relentlessly gloomy! I said this to a writer friend and he said, 'yeah, and'? This judgement was based on her reading of my Tired Waves novella and The Carousel. If there is no room for the intense, claustorphobic and relentlessly gloomy then what sort of a market is it? I agree that, in parts, it is all of these things - and more, but then the same can be said of tonnes of work out there. Hey ho. I shall either wait for this lethargy to pass and try and cram in as much research and other things that I hope will inspire me forward, or plough through it. Me thinks it will be the former.