To encumber is to weigh someone or something down with a physical or psychological burden. You may find yourself encumbered by a heavy backpack or with anxieties. Either way, it's a heavy load to bear!
You can also use encumber to describe something that restricts you in some way: you're so encumbered by your homework load you can’t go to the concert Saturday night. The root, cumber, has several shades of meaning — including "to burden" and "to be overwhelmed."