I second taking up another cross training activity AND listening to your body. When I was sick 5 years ago, I started doing a lot more yoga, which continued, even after I was riding a lot. I also tried swimming, which I hated, but, the point is, I tried.
I have found that short rides, with a purpose often help get me back on track. I spent most of one season and a good part of another riding my hybrid to local farm stands and stores to do errands, as I was building up again. So much so, that later in the second year, I met up with someone to go x country skiing; she brought another friend with her, who recognized me from riding around town, down to even being able to describe my bike and jacket. She asked me if I was car fee.
I got back to where I was by focusing on building up slowly. Eventually, I surpassed my yearly mileage 2 years in a row. I probably won't be able to do that this year, but I think my experience of having to slow down taught me not to worry so much about these things. My average speed and how far I ride don't matter so much any more.