Hi, Jin Thank you for your comment. you say “I'm getting hungry.” when you start feeling hunger. What do you say when you start feeling fun, for example, when you have been adjusted to your new work place, and feeling easier.

no

It does sound a little weird because your meaning is unclear. Are you describing yourself? ex) I'm a fun person to be around / I'm a fun person to spend time with. Or are you describing how you feel about your situation. ex) you are spending time with your friends and you all are having a good time. So then you can say: "I'm having fun."