text: Its the change in the amount of light we get each day, its less during the fall and winter.  Some people also have condition called seasonal affect disorder where they become tired, depressed and sometimes anxious. This is also associated with the amount of light we are exposed to during the fall and winter. Try to get outside more if this isn't possible try going to a tanning booth.  If your worried about the damage from tanning booths use a good sun block and only stay in the booth for a short time 3 to 4 minutes your not looking to get tanned just to get the benifits of the extra light.  There are also special lights you can buy and sit under for 20 minutes a day.  They are expensive though usually around  $400.00  hope this helps.