My mid-PhD blues have been replaced by frantic experimenting and panic, which is much, much better. I got through that rough patch by taking a mental vacation and just accepting the fact that I wasn’t going to get anything brilliant done for a while. I took a few days off and didn’t do any work. For a week or so after that, if something didn’t absolutely have to get done, I didn’t do it. I’d set myself a few (3 or less) small goals for the day and once I accomplished them, I’d let myself off the hook. If I wanted to do more work, I’d do it, but if I didn’t want to, I didn’t force myself. After about 2 weeks of this I started feeling much less depressed about the state of my research and started thinking about some new ideas and directions I could explore.
The timing for this worked out particularly well- coincidentally my bosses were distracted with other things and I couldn’t get access to the equipment I needed until after I was feeling better. When I feel like I’m not making research progress my instinct is always to try to push ahead as much as I can. But perhaps sometimes it’s better to just coast for a bit instead of getting worked up over things that are a very small part of the overall PhD process.