For toddlers between 3 and 5, nocturnal terrors are often connected to the fading out of the nap and more generally to days deprived of usual napping time for very young children.
To understand this phenomenon you must consider the fact that the nap includes the phase of quiet or deep sleep.
The suppression of the nap leads to a deficit of quiet regenerative sleep which is postponed to the night and added to the beginning of the cycle.
OUTLINE of the sleeping construction differences ( coming soon)
The cycle usually composed of a slow wave and REM phase becomes a bigger phase of quiet sleep lasting up to 160 minutes (instead of 90) from which the child struggles to get out of and pass on to the paradoxical sleep(REM).
The micro-wakes which usually pass unnoticed in paradoxical sleep, a.k.a the dreaming phase, appear here after a long phase of quiet sleep and the result are these nocturnal terrors expressed through screams, sobbing, and other involuntary outward signing perceived as a live nightmare for the parents.