The crew (including Spock) has been infected (via sweat) with emotions. Whatever emotions they were hiding — controlling — have come bubbling up to the surface and oh my goodness.
Sulu is running around the ship shirtless, swinging a rapier, and quoting The Three Musketeers.
Kirk goes on a tear about ships being referred to in the feminine because a captain isn’t allowed to look when it comes to women in the crew (even though newbies such as myself know he totally looks).
Spock is a basket-case.
Spock tries so hard to get control back of his emotions as he feels guilty about never telling his mother that he loves her even though it would have meant so much to her as the only Earth woman on Vulcan; as he feels shame for loving his own mother because of his Vulcan upbringing; as he feels kinship for Kirk and feels ashamed of that kinship and feels ashamed of feeling ashamed.
He’s so overwhelmed by everything he feels that he can barely walk straight and it’s reminiscent of any and every time I have ever seen a small child have their heart broken over something we “grown-ups” think to be a completely trivial matter.
It’s such a beautiful performance.