Answer:
What runs around all day. Then lies under the bed. With its tongue hanging out?
What surrounds the world, yet dwells within a thimble?
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.
They're up near the sky, on something very tall. Sometimes they die, only then do they fall.
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.