"Great! You'd be the perfect candidate for this job!" (sarcastic tone; can be used to hand a responsibility from your side to them when you complain about something)
"If you're so good at it, why don't you go do it??" (say it in a cheerful way to avoid conflict)
"Good for you." (nodd your head and just say yeah, yeah. this shuts them up faster.)
These are the nice Fe ways of saying..."Put up or shutup, because right now your all talk and useless."
Take what I say with a grain of salt, because that's all it is compared to the ocean of complexity when it comes to actions and real life.
I advice you not to get in comeback battle with an ISTJ, especially if you already are asking for help. Instead, tell the truth. ISTJs are often good, but oblivious people. You say you had 6 hours of sleep... we think you had 6 hours of sleep. Not that you are dead tired, not that you are having it difficult. We are just thinking you just slept little bit too short.
And we are not actually trying to "best" you, but to give you comfort by sharing the experiences we had, and even try to cheer you up. We survived it, and worse, and so will you. So I'd stress how you are feeling, and not why you are feeling. But still, we are committed to try to find a fix for you.
Sounds to me like you just need to tell him it's annoying. No need for a clever comeback line. Just say 'hey - do you have any idea how annoying it is when you keep trying to one-up me? Please stop. Thanks.' Repeat as necessary.
I like what ScottJames said. Be direct with the ISTJ and be like hey stop trying to one-up me. What is good for me is different than what is good for you.
As a side note, a true ISTJ does not complain or whine, we take what we get, no matter how tough, and we push on. To be honest, I would turn the tables completely on him/her and ask how he/she is doing. That will wig them out and they'll brush it off like its nothing. Almost like reverse Psychology. That how I would handle it. Whatever you do, just be direct.
Me (in the middle of answering how things are going): I am so tired today, 3 nights in a row of 6 hours sleep!
Her: 6 hours of sleep !?!? That’s my usual, if I’m lucky.
It's hard to know her motivations and tone from this.Based on that one interaction, maybe she was just being honest and didn't realize about your health situation. I would just explain it to her calmly about your thyroid surgery. 6 hours is fairly normal for me as well, so I might have made the same comment as her if I didn't know your situation.
If it's the case that she knows and is doing it on purpose, I'd just be like fine, this person doesn't like me so I'll just be on my guard around them, kind of try to dominate them without being overtly aggressive.
i.e. I would grab them by the shoulder, fake laughing, and go something like, Oh man! How do you do it!? (Then to the whole room) Somebdoy get this crazy guy a nightcap so he can get some sleep or he will end up collapsing on us, can you believe he only sleeps like 3 hours a night! (Then to him): Dude seriously, if you want I can cover for you, get some sleep if you feel bad!
Some wierd shit like that anyway is what I;d do, it kind of comes naturally to me as that's how I deal with confrontation. It's an inferior Fe thing, I just don't "get" needless antagonism, so I naturally laugh at it.
If find that Fi users really hate that kind of thing as well. So it would really annoy an ISTJ if that's what you want to do. She'd probably avoid talking to you forever. xD