Yes I do think it is just a strained/pulled muscle but with my mileage it could lead to more serious problems. I try to look at this break as profound rest which will regenerate both mind and body. I cannot remember the last time I had 3 days of rest in a row! My everyday biking, stairs-climbing and callisthenics help my mood not to sink completely.
I am still sleeping 12 hours per day. This weekend I would like to start with cross-training.