My wife recently restarted her fitness journey and after going hard for a week she was grounded by illness over the weekend. What happened? It was a typical case of hard training combined with hard dieting that led to suppressed immunity. I've been a victim myself chasing ridiculous targets like losing a kilogram a day 😣. Extreme I know, but like many of you I wanted results quickly and like my wife, I soon learnt a humbling lesson and that is; progress should be gradual.
What happens when you overdo it?
How should you approach things?
Eat sufficiently to support your training OR train at an appropriate intensity that doesn't exceed your decreased nutrition, but gently helps your weight loss efforts. It's a balancing act that you must get right. Avoid combining hard training with hard dieting. You can go hard in one but keep it moderate with the other.
You just can't "train like a horse and eat like a bird". You're asking for problems.