Do not eat or drink anything so your Sim's Sanity diamond decreases. Once it is no longer filled, your Sim will die and become a ghost. Just call the Grim Reaper and tell him you want to live once again. You need a lot of Sanity points if you want to have a full Sanity diamond. However, there are plenty of choices to pick which kind of Sanity diamond increase to buy. Still, you need the correct amount of Sanity points to get it. Stay as a ghost if you want to be able to float in mid-air. However, all you can do is just float and go in houses or places. To get more Sanity points for when you're living again, go up to a person and scare them. You cannot go to the bathroom or make any food.