Light. Lots and lots of sunlight.
That's what causes Cabin Fever, nowadays known as SAD (Seasonally Affective Disorder) caused by low light, dark houses
and artificial light that is not strong enough or doesn't have the correct colors.
I'd suggest walking outdoors withOUT your glasses, since even window glass can block out the correct sun light. Get some bulbs that claim to have full spectrum light. And look into color therapy. It is even used in hospitals for when a baby is born with jaundice, a liver disease. They stick the naked baby under black or blue lights and cures the jaundice. Think stained glass, and how good you feel in churches that have marvelous colored windows.