Should I be Concerned?

My Fiancé has some health issues. He was in the hospital last week and got home Wednesday. Since then he has not been sleeping well, has been very grouchy. He isn't really treating me differently, just a little less affectionate. All understandable. But this morning he completely flipped out on my cousin over something pretty small. I am worried there are parts of himself he has been hiding from me.

How should I talk to him about this? Should I be worried that his behavior will get worse?
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Thank you both for your responses. I agree with you both, so I calmly talked to him about it. As it turned out, he saved the messages from the fight and she was just as much at fault as him. I asked that in the future he keep his temper with my family :)
Should I be Concerned?
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