Firstly remember that, assuming you're only human, it's okay to have an off day. As you say you're normally enthusiastic, my advice would be to figure out what's dragging you down. Then spend five minutes ranting about those negative points, to get them out of your system.
Then, either fix them, or get over them and move on. Staying in negative space for any period of time will only harm, never heal.
Break up your new client calls with one to an existing client. Getting feedback on what is good or needs fixing can help keep you informed. If you made one client happy, you'll be motivated to have more.
I know you want to maximize your efforts, but getting a cold call early Monday morning is not high on my list. I'm usually trying to get caught up and plan my week.