I've noticed a trend lately with a lot of my clients. To be truthful, it's a problem I see mostly with my female clients. It's not sexist, it's a trend. I'm pretty much doing statistics here!
This trend is that my clients want to train and train and train, with very little recovery time. Yup, some of them routinely go 6 or 7 days straight without taking a rest day.
While this isn't an awful problem to have (better than not even getting off the couch to go to the gym once per week) it's still a problem. If you train and train without giving your body any time to rest and recover, you're going to eventually break down. This break down could be mentally or physically, but it will happen eventually.
You could be tired and not have your mind in your lift that day. You try squatting with minimal focus and end up dumping the weight and hurting yourself. Or maybe your mind is super sharp and you want to crush this weight, but your body isn't up to the task anymore and you hurt yourself.
Beyond that, your body will just stop responding well to training. You get filled with cortisol and other stress hormones and your body stays in a constant state of catabolism. You stop seeing gains in strength or body composition, so you train harder in the hopes of over-coming your "funk". This is, of course, a vicious circle that just results in more fatigue and fewer results.
Take your rest days (and by "rest" I mean just that). Go home from work and sit on the couch and watch TV or read a book. Don't go run hill sprints or do stadium stairs. Don't do a light recovery workout. Just rest, please. Eat some good food and get some good calories into your body. Remember that you're not going to reach your fitness goals in one workout. Time takes time! Fitness and being strong is a lifelong goal, so plan to be able to train for that long.
Have a great day, and consider NOT lifting something heavy today!