Very heavily, without subtlety. For example, If he doesn't like your work, he'll come down on you like a ton of bricks. This expression, often coupled with COME DOWN ON (def. 1), replaced the earlier thousand of brick or hundred of brick. The allusion in all these is to the considerable weight of such a load. [Early 1900s]
American Heritage Idioms
Phrase(s): *like a ton of bricks Inf. like a great weight or burden. (*Typically: fall ~; hit ~; hit someone ~.) • Suddenly, the truth hit me like a ton of bricks. • The sudden tax increase hit like a ton of bricks. Everyone became angry.
McGrawhill's American Idioms And Phrasal Verbs