HIIT is super tough. I'm a 24 year old athletic guy and I've had times when I'm on the ground almost passing out from HIIT. Maybe if you're having THAT MUCH trouble with it that it becomes unbearable, switch to LISS for a little bit so you can build some more cardiovascular endurance and then come back to HIIT?
That's what's worked for me in the past. I don't do HIIT anymore unless I need it for a cut and I can do like maybe 15 minutes of it and then I just want to die. However, I have, several times gotten through the insanity HIIT program with Shaun T. (before lifting) and can say I was in the best shape of my life back then
It's all about the mindset you adopt during the cardio. If you're racing to the bathroom, you're not stopping no matter how many stairs left. If you're running towards a loved one you haven't seen in years, nothing's gonna stop you. I just try to access that kind of mentality to keep going even when it gets a little tough to breathe. Another good trick is thinking of the bigger picture. All those cliche statements like "this is how it feels to carve out your new body", generally bring you back to a larger picture that remind you why you're doing it and how much you really want those goals.
Best of luck! hope this helps!