Sleep states are not a switch you just flick - that be equivalent to you pulling the power cord. Even in the highest, most power hungry sleep states the kernel

Sleep states are not a switch you just flick - that be equivalent to you pulling the power cord. Even in the highest, most power hungry sleep states the kernel has to pause everything first, power down all the other hardware (otherwise you'd still have you WiFi card and GPU running full tilt), configure what will interrupt the CPU sleep and finally start it. On the other end it has to set everything back up, reinitialize all the other hardware to be in the same state as before, and finally start running user space again - pretending nothing happened even though the foundation was removed and rebuilt. The only real difference to full hibernation - where the machine is powered off entirely and the kernel restores system state from a snapshot it wrote to disk - is that the RAM state sticks around and that the CPU executes the kernel again on wake instead of dropping to the firmware boot sequence. Without that boot sequence, hibernate would basically be indistinguishable from suspend - an Phoronix article some years back talked about how Intel tuned the kernel to get from cold boot to full interactive UI in 300ms for automotive usecases.