After losing 60 lbs, you probably are running on not much in the way of muscle and liver glycogen stores, which you would have depleted a fair bit in the first few weeks of weight loss. When you exercise your body expects that to be there for precisely this situation, having to suddenly crank out extra food for your muscles and heart and everything else. You may not have measurably low blood sugars but your body is pretty likely to have a few complaints about you doing that to it, having to put out extra energy with minimal glycogen, there is nowhere it can easily get this extra energy from. Your body can use fat instead for this but my understanding is you need to train it to do that, and is not going to suddenly get better at it, but will if you slowly increase exercise levels.
So your body whinging that it has no food to do that exercise tells you to stop by making you feel nausea or faintness or extreme fatigue. It is not going to kill you to keep going but your body will complain. You probably do not have a lot of choice but to listen to it and build it up slowly unless you can improve it with food before exercise, otherwise you might actually faint.
I have definitely had this from exercising while dieting years ago both nausea/vomiting and fainting or faintness.
Your body might be happier with some carbs pre exercise, but you are probably going to have to experiment a bit to find out what food or fluids help or make it worse and the best timing. It does improve with training.