Castiel wasn't registering his own exhaustion, mostly because it was difficult to separate it from how tired he already was from having not slept in two days, and also because he simply willed himself through anything of the sort. But he didn't want to push the other two if they were wearing out, so he nodded slightly. "I believe the experiment itself was a success, so there is no need to risk any of us any farther." He nodded again at them both, this time in thanks for their help.