Plato has Phaedrus say: You will soon break the bow if you keep it always stretched.
When the initial motivation is extremely high or the external and internal, personal expectations are too demanding, often physical and mental burnout are observable. What is happening in management can be compared to a similar phenomenon in sports: overtraining, plateaus, physical burnout, and fatigue are the results of the triumph of will over sensibility. The cure against burnout and overtraining is very simple: stop immediately and rest.
Excessive training, trying too hard, or monotonous routines that don't challenge the mind or body lead to overtraining syndrome with symptoms that are hard to recognize and differentiate from mere temporary exhaustion or psychological causes instead of effects.
Overtraining may lead to training plateaus, the body cannot catch up regenerating itself and gets stuck on a mid-level that is achievable without adequate rest. Overtraining is the result of weeks or months of wrong training, you're not going to burnout after a couple of days or some high intensity training.
An effective strategy to avoid and to prevent overtraining is to listen to your body's needs and its instincts. It's all too easy to override pain in order to achieve the next promising and potentially rewarding goal. The body as well as the mind need rest. Growth and improvement take place while not training, while at rest, between workouts and after work. Hard work is definitely necessary but the moment it becomes mindless it is a sure sign of becoming insensible and therefore against nature's requirements.
It is vitally important for eventual success to balance and level the eagerness in the beginning and focus on maintaining the discipline through the initial motivation and the lows and the highs and the plateaus.
Consciously relax and release all the tension from time to time. Make no exercise a dedicated exercise and count the non-reps, e.g. try to statically hold nothing for the intended duration. This special exercise is the only exercise that let's you grow while still working on it...
The same holds true for corporate executives: rest consciously without working at all. Schedule an amount of time where you absolutely do not work. Consciously dedicate this time to not working at all. As a side effect, you will notice how, perhaps unexpectedly, your productivity will go up. Your energies will replenish and you will gain new clarity.
Enjoy every moment of your recovery, as much as you enjoyed, with all your heart, work until crashing.