I think the line is actually somewhat subjective. Getting dangerously drunk used to not be a crisis for me. Not at all. Now it's a crisis because I don't actually want to die and I do scary things in blackouts. Right now if I even think about drinking, it is a crisis for me.
But what you said fits for crisis for me too generally...not being able to do work/school, constant suicidal thoughts. I haven't been suicidal for a long time and I don't actually think of my self harm as a CRISIS! crisis. It's a "crisis" where I need to reach out somehow, find safety, contact my therapist, get grounded. For me the major crisis are the ER types or ones where I'm putting my life in danger, which I've done a lot.
So for me there is stress, meltdown, crisis, and major crisis, all on some sort of continuum that is not very black and white. The last couple times I went to ER, I call 911 myself. There's a chance I would have lived okay on my own and woken up the next day, but I was scared. But in the past I would have kept drinking and not considered it a crisis at all...though in these circumstances when I get to ER I usually have alcohol poisoning, oxygen issues, acute hypokalemia and other signs of bodily crisis requiring fluids and heart monitors. But even when I did end up in ER in the past, that wasn't even a crisis. I went back to school/work like nothing happened...made no effort to find better support or change anything.
So while it would seem like putting ourselves in danger would represent a crisis, it's pretty subjective. Putting our lives at risk really IS a crisis, but I have absolutely felt that as not the case in the past. I'm glad I see crisis situations more clearly now because it means I care.