Adaptation
Adaptation is the process by which transitions between sleep schedules happen. Usually, we think of them in stages, although the stages are really just different levels of symptoms, with the underlying processes of repartitioning (& alignment) and compression happening pretty much continuously, and deepening and ls-compression happening during stage 3 only.For an overview of what to do for adapting to a new schedule, read how-to-adapt.
For an overview of signs of a successful adaptation, read adapted
Stages
Stage 1
Stage 1 is the stage where little to no sleep deprivation is present, leading to very little sleepiness, if any, and what feels like a glimpse into the delight of being adapted. After a while though, this bliss turns into Stage 2.If sleep deprivation is present at the start, stage 1 cannot exist as it is defined by a lack of it. This means that the time usually spent in stage 1 is spent in 2 and 3 instead - without improving speed for most.
Stage 2
Stage 2 is where you start to notice sleepiness. You may start to experience slight loss of energy, and some tiredness. You probably begin yawning during the day.Stage 3
In the 3rd stage, sleep deprivation kicks in, microsleeps may become relatively frequent unless fought against. In general, to stay-awake becomes quite difficult, and avoiding oversleeps in general may become a nightmare. In this stage, it is absolutely vital to have a good alarm strategy, as waking up without them may prove impossible. Even with them, zombie-mode can mess you up, so multiple alarms are encouraged. Here, alignment becomes noticeable and some sleeps may start to feel different, which can make falling asleep a breeze or very difficult seemingly randomly.When more sleep deprivation is present at the start of adaptation, this or stage 2 will be the first stage instead of stage 1 - but speed is not improved.
There is a hypothesis that creatine helps alleviate stage 3 symptoms, but there is a chance it may prolong stage 3 also/instead (we do not know yet).