Occasionally a crown or filling may come out and leave a space in your tooth. This will feel enormous to your tongue, but when you look at the piece that is lost you will see it is often quite small.
Please try and keep the lost piece to show to your dentist, as this may be helpful. Do not panic, there is often little or no discomfort, although in some cases your tooth may feel sharp and be sensitive to extremes of hot or cold.