Performing enthusiasm in the workplace

....does it work? I feel pretty subdued most of the time but I give real good interview, and things start to deteriorate once my coworkers realize how tired and nervous I am. I'm onboarding now and the person guiding me through it is very chipper, like on a level I thought was socially frowned upon (godspeed to you ladies who end a sentence with 7 exclamation points). do you think we can fake it til we make it, at least in this way? it does actually seem like a lovely workplace as long as I maintain my boundaries around overworking!