At first I thought I was going to pass-out, then I felt chills, then I started trembling, and then I vomited about 6 times over the course of a minute. Then 45 seconds later, I felt fine.
If you were feeling fine 45 seconds later, I'd say you haven't hit "the limit" yet.
About 12 years back I was in a locker room for a wrestling weigh in. I had about 7 or 8% bodyfat at the time and was going from 134lbs to 125lbs. I did that for a couple of weeks without any real problem.
Then one Friday a buddy is checking my weight on the scale. I've got my glasses off so I can't read the numbers. He tells me I have a quarter pound to go. I slide off the scale and sit on the locker room floor putting my drawers, sweatpants, t-shirt, etc back on. I didn't even manage to get dressed.
I fell over on my side; didn't really say anything I guess. Somebody did a "WTF dude?!" and I just said I was tired and needed to take a rest. Older guys on the team ran like hell out of the room to get Coach.
Coach gets there, probably within 30-60 seconds, and I'm curled up in a ball. Every major muscle in my body is cramped up. Knees are at my chest, hands look like bird beaks, and my speech is so slurred I sound like a drunken mongoloid.
Coach has a few guys toss me up on a table and sit me upright, tells somebody else to get some water. The dude that weighed me earlier pipes up, "No! Throw him on the scale! I was just f-king with him, he made weight!" Dick. We're still friends, BTW.
Anyway, Coach nixes that idea right away. He's pulling my arms down and spreading my fingers apart and then telling me to hold onto my knees. Didn't work. I couldn't keep my hands from turning into bird beaks. Plus I was pretty incoherent. He kept asking me how I felt and I kept saying, "I'm just tired. It's like at the end of a race." We started getting some water in me, and I had some food I planned to eat after the weigh in handy too. I shoved 5lbs of food and water, mostly water, down my throat in the next 30 minutes.
If there's a level of exhaustion beyond that, I don't want to go there. That was scary enough.