Sleep deprivation has been linked to anger, anxiety, and depression, as well as a host of other mental health issues. A study has shown that moderate sleep deprivation is basically the same impairment as maximum legally permitted levels of alcohol intoxication.
A normal human needs 7-8 hours of sleep. Any less than that, and sleep deprivation will kick in after a while. Any more than that, and they may feel drowsy and tired.
There are several tranquiliser medications to help sleep short-term, such as Zopiclone, however these are addictive and can form dependency. One way of solving sleep issues quickly is staying awake until the next bedtime, however this is quite difficlit. Caffeine and power (15-20 minutes) naps may be used, however this depends on the individual on whether this is effective.
Another way of fixing issues, if possible, is to move the bedtime by 15 minutes back or forth daily. This is a slow way of fixing sleep, but may be the last resort.
There is evidence to show that blue light may disrupt sleep patterns, such as the ones found in screens, so software such as f.lux or Night Mode on iOS/Android may be used.
For some people who are not hypersensitive to sounds, calming music may be used. Try ASMR youtube videos as well, as they have been found scientifically to boost mental health and encourage sleep.
Finally, while often tried already, sleep hygiene is important and not to be omitted.
If all fails, you may have a condition that makes it difficlit to sleep. See a doctor for physical health issues.