I felt tired when I got up, but I went out running anyway. After a quarter mile, I turned around and walked back. I could have continued and probably felt better after I'd warmed up, but I decided it was better to rest today and increase my chances of having a good run tomorrow rather than risking losing both days. The temperature was about the same as yesterday, so that wasn't a factor in my being tired. Also, I slept well last night. I had a good running week last week and yesterday, and I think my body just needs more rest.