This is a common issue especially for newer freelancers, work drying up. The trick is to be able to predict these dry spells as best you can. Often your client base will be made up of a mix of people making regular content but some may make 2 projects a month, some 1 project every 2 years. Having a wide array of clients and project types should keep you working all year round.
For me the quieter times are often by choice after 5 years and 400 projects. I pretty much just stay on christmas holidays until mid January and then see how Feb and March shape up as things get going. Then around August everything dies for a little bit (including myself) as i take a mid year break.
Let me know in the comments what you do and feel free to subscribe to my YouTube channel and hangout live with me sometime.