I can completely relate to this feeling. When I skip my workouts, I feel terrible. Especially if I had the time, and I chose not to get off my bum and do them. Conversely, when I wake up in the morning after a tough training session and my body is sore; I smile. Yes, it hurts like you-know-what BUT it means I put some work in and my body is changing.
There's no point in regretting something that you have control over. Just do it, like Nike.