It's almost like letting your body nap while you are completely awake.
While people are
layin, many times they listen to music, talk to friends, lay with pets, spoon, or for the full effect they do nothing at all.
EX: In the summer I'm always layin in
the AC with
my puppy.
EX: When you hung out on your bed all day and your friends asked you what you did all day you might respond "I was layin."
Lay = the actual action
Lay Sesh = The period (or session) in which you were layin