Rav Shmaryahu Greineman zt”l was once in the home of his brother-in-law, the Chazon Ish zt”l, when he suddenly heard a loud bang coming from the Chazon Ish’s room.
He immediately ran into the room to see what happened and found the Chazon Ish lying on the floor with his hands and legs outstretched. Rav Shmaryahu ran over to him and asked, “What happened?”
The Chazon Ish replied, “Don’t worry. I always learn until I have no strength left. I usually make sure to leave over just enough strength to make it to my bed. Today, I made a mistake with my calculation and didn’t have enough koach to make it.”