Hello, I'm back again lol

So can you tell me if I'm over reacting or if this is blatant discrimination?

Back story, I work for USPS, I deal with heavy packages among other things. I have worked every Sunday for 2 years which is purely Amazon day, and then plant mail day. A Lot of heavy lifting. I just had 75% of my lungs worked on in just the past 3 months due to severe lung disease, which is highly documented and FMLA protected, as well as seen as a legal disability in my state.

So there's a coworker who religiously is late by 1-4 hours every single day, no one blinks an eye.

I come in today at 5:26, schedule time is 5:30. She comes in at 6:22 and scheduled time is also 5:30.

I told my boss before we started today that I am having a lot of breathing issues today and I really need help with my packages, he said "okay, **** will help you"

So we start on our work and not even an hour later, the boss comes and asks us why we're not done yet and there's only 800 packages between 2 people being thrown in an hour and says this will affect everyone else's finish time as well. My helper is a veteran who also has documented back issues, so basically 2 broken people trying to work as a team. I said "Well, it probably has to do with ------ coming in an hour late." My boss said "that's irrelevant, if you're not gonna go faster then ill just take away your help."

I and my help came early today and she was an hour late, but that is irrelevant to the time everyone will be done. I then told him I need to leave because I was getting worse, and he replied with, "well don't you have an inhaler you can take?" I said "yeah, it doesn't help, that's the reason for the surgeries."

so I left and went straight to urgent care and had to have a steroid shot as well as dose of steroids to take for this week and 3 days off. I check my online time card thing and since I am contracted to work for 4 hours a day (I normally work 10), I left at 3:46 hours. My boss is suppose to ask if I want annual or LWOP -leave without pay, which he didn't. he just threw me in LWOP.

It's only 14 minutes, I know. But it's the principle of the thing. Am I over reacting on feeling like that was 100% disability discrimination? Everything has been medically documented, I JUST had double lung surgery not even 2 months ago and have only been back at work for about 2.5 weeks.