You may be employed in a company that makes you work either night or rotating shifts. Instead of the usual working hours of 8 AM to 5 PM, your job demands you to be present in the wee hours of the night. This causes you to have troubles in your sleep patterns and experience excessive sleepiness during your work hours; therefore, you may have Shift Work Sleep Disorder (SWSD).
In SWSD, you may have difficulty falling and staying asleep, and has the tendency to be sleepy at work. The number of hours you are asleep may also be shortened to 4 hours instead of the normal 7-9 hours of sleep which your body needs. You may also have poor quality of sleep and wake up feeling unrefreshed making you feel tired at work thus affecting your work performance. These symptoms persist as long as you are working on shifts. SWSD usually go away once you go back to your normal sleep time; however, for some people this may not be true. In these cases, you may want to consider visiting a sleep specialist.