Do fish lay at the bottom of the tank when they lay their eggs?

Not normally.

sometimes, but did you know minnows don't lay eggs, my brothers n sisters n me n mom n dad watched a minnow have a baby fish, and my mean brothers cut one minnow open b/c it wuz dead and we saw...

Until you remove it...it's most likely dead.

because the fish may be sick and does not have the sternth to swim.

They like sleeping in darker areas.