It would be wonderful, albeit boring, if life proceeded smoothly all the time. On the day of the interview, you intend to be well prepared, rested, up early, and in good form. What if you spill breakfast in your lap, jump a red light on the journey, and arrive late to find your manager waiting for you? A bad start to the day! All is not lost; you can learn to switch to "performance mode".
Have you observed how athletes take a minute to get into the zone before performing? Here is a mental trick I use when I have to perform and don't feel like it:
Sit quietly and remember how you felt when you were in top form, and practice recalling those feelings.
When you do, make a physical link to them.
Choose a physical link that is discreet so you can trigger it when you are not alone.
I make an O by digging my thumbnail into my right forefinger. Whatever your trigger, recall the feelings and jump into performance mode whenever you need it.
Practice it so you can jump at any time.
The next step is to prepare the candidate, to relax them so they are ready to be interviewed.