Sending good thoughts for Gavin. Lethargy can be a Lyme symptom--it was always the first sign Barkley's Lyme was flaring, and that can also affect their appetite. If it doesn't improve in the next day, I would have the vet see him and do a Lyme test. Hopefully if there's any question they'd do a round of doxycycline. Most vets will do that just to rule out Lyme even if the test is negative. A dose or two of doxy improves them almost immediately. Give your boy a gentle pat for me.