Extrinsic type

Two of these disorders are extrinsic (from Latin extrinsecus, from without, on the outside) or circumstantial:

§  Jet lag, which affects people who travel across several time zones. Seen in people who travel across time zones, symptoms include excessive sleepiness and a lack of daytime alertness.

§  Shift work sleep disorder, which affects people who work nights or rotating shifts. This sleep disorder affects people who frequently rotate shifts or work at night.