is complete emptiness, nothingness unstable in physics?

I believe you are referring to "quantum jitters". Even in complete emptiness vacuum fluctuations spawn pairs of particles that quickly annihilate . They cause a momentary disturbance in the EM field. So, even free space isn't completely empty.

In a physical theory in a false vacuum, the system moves to a lower energy state – either the true vacuum, or another, lower energy vacuum – through a process known as bubble nucleation. In this, instanton effects cause a bubble to appear in which fields have their true vacuum values inside. Therefore, the interior of the bubble has a lower energy. The walls of the bubble (aka domain walls) have a surface tension, as energy is expended as the fields roll over the potential barrier to the lower energy vacuum. The most likely size of the bubble is determined in the semiclassical approximation to be such that the bubble has zero total change in the energy: the decrease in energy by the true vacuum in the interior is compensated by the tension of the walls.

The possibility that we are living in a false vacuum has been considered. If a bubble of lower energy vacuum were nucleated, it would approach at nearly the speed of light and destroy the Earth instantaneously, without any forewarning. Thus, this vacuum metastability event is a theoretical doomsday event. This was used in a science-fiction story in 1998 by Geoffrey A. Landis, and in 2000 by Stephen Baxter.

You may be surprised to learn that science does not recognize nothingness as being a possibility! The definition of a void could be interpreted to mean this and even though that word is used in physics to describe the space between walls of galaxies, physics says there is at least one particle of matter in every cubic kilometre of that void.