What is that movie? it is about some man who is slowly turning into a monster (possibly a boogie man?)?

It is about some black man with dreadlocks and he starts turning into a monster and his finger nails get really long and he starts going crazy. Some girl is trying to help him. The man then takes her brother under his bed and ties him to something. Under the bed is another land, a crazy land with things flying and a giant sandwich, ect. The girl goes under the bed to save her brother. That is about all I can remember. The movie was made probably in the 90's.