The see-saw of having a creative vocation is a never-ending cycle. Inspiration soars, and then just as quickly disappears. Opportunity knocks, and then suddenly becomes silent. Our world revolves around the unpredictable ups and downs; income instability, creative surges and blocks, successes and failures.
One of the most valuable lessons for anyone in a creative vocation to learn, is that these peaks and troughs are a normal part of the game. What's important is to hold on to the knowledge that the down will end, and the upswing will come. Not by sitting back and doing nothing, but by continuing with a sense of momentum. Sometimes this momentum draws us into new enterprises and new ideas, which can then lead to new inspiration and new opportunities.
When you're in a downward swing, remind yourself that you've been here before, and that there is an upswing ahead. Do whatever you need to do in the meantime...re-evaluate your projects, do some housework, catch up on some admin, send stuff to people, reconnect with previous contacts, make new contacts. Sometimes simply doing something completely different helps, with an ultimate distraction which can get things flowing again. The important thing is to not stand still. Pausing is healthy, but doing nothing at all besides wallowing will only feed negativity.
Remember the law...for every action, there is a reaction.