Good Riddles

Question: I am almost nonexistent through sorrow, yet am frequent through happiness. I have no contact, yet I am contagious. What am I?

Question: You put me on a table and cut me, but you don't eat me.

What am I?

Question: 1 is 3, 3 is 5, 5 is 4, 4 is universal. 2 is 3, 3 is 5, 5 is 4, 4 is universal... how is this possible? (What is the rule to this sequence of numbers?)

Question: There was once three trees. The first tree did whatever the third tree did, and the third tree did what ever the second one does. What happens if tree number two gets cut down?

Question: I run over fields and woods all day. Under the bed at night I sit not alone. My tongue hangs out, up and to the rear, awaiting to be filled in the morning.

What am I?