I too have been puzzled by the energetics of gravity. As a matter of practical science, we can observe that a mass, on approaching a gravitating body, experiences a force in the direction of its motion, which constitutes work upon the body (as seem by an observer on the gravitating body), and if that work is removed from the system as by friction and thermal radiation, the energy of the system ends up less than what it was before. Accordingly, we observationally conclude that the energy of the system is less when the bodies are close together, and on that basis, assign to the lower altitudes a lower gravitational potential. But does that mean we have literally negative energy? That involves delving into some difficult areas. One is the quantum equivalent of energy, namely frequency, in which a particle of energy E has a frequency of 2 pi E/h . There is reason to think that the correct E in this formula is the mass of the particle (special relativity seems to require that). For a particle to have literally negative energy, the mass would have to be negative, which has the curious consequence that not only must the quantum frequency be negative (resulting in a reversed complex exponential), but its mass must be negative also. But if its mass is negative, then it creates repulsive rather than attractive gravity. No such thing has ever been seen of ordinary matter; however if we consider the gravitational field itself as having an energy, then it itself may generate additional gravity. That contradicts Newton's formulation of gravity, but is not necessarily in error because Newton's formulation of gravity is an imperfect approximation valid only in the limit of fairly ordinary circumstances. Does a gravitational field, being of negative energy, generate additional gravity that opposes itself? These are the kinds of questions that can't be answered without digging into the messy details of general relativity.