Jacking your husband off: Do your muscles get tired from doing it sometimes, too?

My husband is wonderful and I love catering to him. But, sometimes my arm(s) & hand(s) are tired from Jacking him off so much. And lately I've been saying no or no I don't feel like it when he asks me. I feel bad because I KNOW it makes him feel bad to hear me say no. He will say, "okay." ***looks kind of sad, goes to sleep***

I'm thinking, " hold up now, I didn't say I wouldn't have sex with you instead!" (We have sex a lot too, so it's not like he's not getting any booty)

My arms just get so damn worn out, they need time to recharge lol. I've told him this but he kind of takes it as some sort of rejection or something.

Does this happen to anyone else? Do you have any advice?