What is that strange glowing orb in the sky and why does it burn?!

My room's curtains are quite heavy and keep any daylight out of my room. So, this morning, after I woke up and went to open my curtains, I was suddenly hit with a brilliant beam of light that sent me hissing and screaming into a corner of my room.
It took me several minutes before snapping out of this confusion and figuring out what caused this violent phenomenon. However, I apparently didn't remember what you're supposed to do with sunny days and spent a good chunk of my day doing work on the computer. I finally realized my mistake, and still not quite getting it, I laid in the sum beam shining on my floor for about an hour.

It was then that I remembered you're supposed to go outside when it's sunny and like 12C (53F). Needless to say, by the time I made it outside, the sun had dipped below the skyline.

I now have a reminder next to my window for the next sunny day:

GO OUTSIDE IF IT'S SUNNY, YOU IDIOT.