You could get sick from moldy mushrooms if the mushrooms are really moldy or slimy.
But mushrooms can have some mold that is edible and not bad to eat.
Some types of mold are healthy for you and are actually a medicine.
Some mold on some mushrooms is due to the toxin created by the fungi which is what mushrooms are and it's usually safe to ingest the mold on the mushrooms.
As long as the mushrooms smell good and are not slimy then the mushrooms with mold on them are safe to eat and will not make you sick.
I've eaten moldy mushrooms before myself and nothing bad has happened at all.
The worse thing that would happen is you get a stomach ache.
Mushrooms when kept in the fridge will last for 3 to 4 days.
After 4 days the mushrooms will start going bad and should be thrown out as they can grow bad bacteria.
If you notice a bad smell to the mushrooms or they are getting slimy or have changed color then throw them out as they have gone bad.
You can freeze mushrooms and they will last longer.
When frozen the mushrooms will last for up to 6 months before they go bad.
I will sometimes freeze mushrooms to use later in soups and stews or in baking and they've lasted up to 6 months in the freezer.
The freezing temperatures of the freezer prevents bacteria from growing on the mushrooms and other food so they last longer.
You can put the mushrooms into a freezer safe container or Ziploc bags or freezer bags.