In my freelance days, I felt structure was still important. Still go into the office at the same time, and focus on work-related things, so you don't become rudderless.

This is easier said than done. When I was super-busy, I would always say, "I wish I had a free week where I could teach myself X, or read that work-related book, etc".

But when those quiet weeks arrive, the panic sets in, and you find yourself needing to drum up new business above all else, even though, more often than not, you will get that email entitled "Availability?" and it's all fine again.

So my advice is, [A] don't panic, but [B] have a structure for when you inevitably panic :)

Do something work-related at the beginning of each day (catch up on blog posts, send some keep-in-touch messages to clients, sort your expenses out), then reward yourself with fun stuff (gardening/knitting) later in the day, and trust the work will come in.