I get irritated because even though it's nice to be thought of, I get a feeling certain people ask me if I'm okay more for their own selfish need. They need me to be okay. They need someone to vent to. They need to be able to help me when I'm not in a good place. When they can't fulfill that need for me, they get irritated because I didn't allow them to help. Like I'm never allowed to feel bad as long as they are there. That's overbearing.

And all for what? Why is it so difficult for them to comprehend that they can't help me in the first place?

So my suggestion is actually not to continue pestering questions of "are you okay?" but rather to do little things that show the other person is being thought of. Get them their favorite food. Pick some wildflowers from the park and leave them on their desk with a kind note. THAT is something that can appreciated anytime from anyone. And it's not overbearing.