3 steps in learning and memory process are: acquisition (introduction of new memory), consolidation (memory becomes stable) and recall (ability to access information). While acquisition and recall are done during wakefulness, memory consolidation occurs in sleep.

There are 2 types of memory:

1) Declarative memory – remembering facts and events, which can be stored and recalled.
2) Procedural memory – motor memory or remembering how to do things.

Processing and consolidation of declarative memory occurs in SWS (slow wave sleep) when 'pruning' or removal of unnecessary details take place. Temporary to long-term memory transfer also occurs in SWS. Sleep also plays an important role in the ability to learn new tasks, requiring motor coordination. REM sleep plays a critical role in consolidation of procedural memory like riding a bicycle, dancing, playing a piano and writing.

Sleep loss affects learning and memory. A tired brain slows down, so that you can fall asleep easily. However, slower function during daytime results in increased reaction time, and reduces attention, reasoning ability and decision making skills.

Stress hormones increase when you do not sleep enough, leading to increased stress levels. Sleep loss also increases negative emotions like irritability, anger, fear and sadness, while it reduces positive emotions like happiness, excitement and contentment.

Activity of the prefrontal cortex (PFC), which is required for processing emotional information is also reduced with sleep loss. A properly functioning PFC helps ensure appropriate behavioral responses to situations. Therefore, sleep loss increases your chances of acting inappropriately in a given circumstance.

2 hormones (Ghrelin and Leptin) regulating hunger are affected by sleep. Ghrelin increases appetite, while Leptin reduces it. During wakefulness, you will experience hunger once every 4 hours. For instance, if you eat breakfast at 8am, you will feel hungry by noon (lunch), then at 4pm (snack) and by 8pm you will be hungry for dinner.

You are able to stay asleep for 7 – 9 hours at night, without feeling hungry due to reduced Ghrelin and increased Leptin levels at night. With sleep loss, ghrelin level increases, while leptin level falls, leading to an increase in appetite and hunger. Therefore, people who sleep less are more likely to eat more and gain weight leading to obesity.

SWS is the most restorative stage of sleep. 75% of GH (growth hormone) is secreted by the pituitary gland during SWS in the first 1/3rd of the night. GH plays an important role in the growth of children and in tissue repair and restoration. GH also works to rebuild your body and muscles from the stresses of the day.

Even if you miss 1 or 2 days of sleep, you will have SWS rebound on subsequent nights. However, chronically irregular or disturbed sleep will affect growth and tissue repair.

When you sleep, your immune system releases cytokines. Cytokines help promote sleep and are important in preventing and fighting infections. Sleeping less will reduce cytokines, increasing your risk of becoming sick. Studies have also shown that the flu vaccine becomes less effective when you sleep less due to a reduction in your body's ability to produce immunoglobulins.