Turning to stone and going back is not possible, as it requires changing the atoms making up the body of the victim.
A similar result can be however be achieved if the injected toxin create a state similar to rigor mortis: all the muscles (well, only the voluntary muscles in this case) becomes rigid, so that the victim is alive but paralyzed like it was stone.
After death, respiration in an organism ceases, depleting the source of oxygen used in the making of adenosine triphosphate (ATP). ATP is required to cause separation of the actin-myosin cross-bridges during relaxation of muscle. When oxygen is no longer present, the body may continue to produce ATP via anaerobic glycolysis. When the body's glycogen is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges.
Additionally, calcium enters the cytosol after death. Calcium is released into the cytosol due to the deterioration of the sarcoplasmic reticulum. Also, the breakdown of the sarcolemma causes additional calcium to enter the cytosol. The calcium activates the formation of actin-myosin cross-bridging. Once calcium is introduced into the cytosol, it binds to the troponin of thin filaments, which causes the troponin-tropomyosin complex to change shape and allow the myosin heads to bind to the active sites of actin proteins. In rigor mortis myosin heads continue binding with the active sites of actin proteins via adenosine diphosphate (ADP), and the muscle is unable to relax until further enzyme activity degrades the complex.
The toxin has therefore to interfere with calcium pump and ATP production.
Its metabolites shall then have hallucinogenic effects, which, given the set (prolonged paralysis, fear and panic) are surely going to induce a bad trip.
