Punky Cocker, any ideas?

My ECS Sophie is not acting like herself, and I'm stumped. We were on vacation last week at the beach. She ran like a maniac chasing her ball for quite awhile (30-60 minutes) a couple times a day most days. She runs very fast and long, but takes breaks herself when she is "tired". We came home sunday and she seemed fine. Starting monday or tuesday am, she has been punky--seems overly tired, doesn't want to jump on the couch or bed, and walks up the stairs rather than running, and seems really anxious (shaky) until I pet her and calm her down. She isn't limping on any one limb, and she is eating, drinking, eliminating normally. There's no point tenderness or pain with moving her joints that I can elicit.

As background, she had luxating patella surgery 1 1/2 years ago, did well afterwards, and has had no recurring limping of either back leg. It was pretty obvious when she had the knee problems.

She is a fairly "highly strung" dog who is very, very attached to me. Of course I had to go back to work this week, so she is not too happy about that. Her home routine is the same as usual, but I'm wondering if after a week of vacation together, she is overly bummed about the home routine.

I'm also wondering if she might just be sore from all the excercise she got on vacation? It was probably more that she had had on vacations in the past (she's 3 1/2 now).

Of course, if she doesn't perk up we'll go to the vet, but she is quite afraid of the vet (surgery experience, plus being a general shy dog) so I don't want to over react if its not neccessary.

Any thoughts?

Jake's mom