It is not uncommon for crowns and bridges to get dislodged, especially if you have had them for a long time. The good news is that it is possible to put the crown or bridge back in. While losing a bridge or a crown can be quite distressing, it is rarely a serious emergency. As long as you take measures to protect the tooth and go to the dentists as soon as reasonably possible (a delay over the weekend, if your dental office is closed, should not be an issue as long as you are not in pain) the dentist should be able to fix the problem.
If you lose a crown or a bridge during normal office hours, head to the dentists immediately. If you lose it during the weekend, or a public holiday, try to preserve the damaged part until the dentists opens again.
Clean the inside of the fitting and try to remove any cement that is in there. Check that the crown or bridge will sit back inside the mouth comfortably. Remove it again and then carefully dry the inside.
Try to dry your tooth as well. If possible, use some over-the-counter temporary cement to re-seat the crown and hold it in place. If you have crowns or bridges consider keeping some of this in your first-aid kit because it comes in very handy. If you have lost the crown or bridge you can use the cement to act as a temporary cover to protect the exposed surface of the teeth.
If you were in pain, then covering the tooth again should help to reduce the pain. It is OK to take over-the-counter painkillers (assuming, of course, that you do not have an underlying medical condition and you are not taking any other medication).
Do not, under any circumstances, use standard household glues to try to repair your teeth. Many of these glues are toxic and even the ones that are not explicitly toxic could cause serious damage to your teeth. If you cannot use temporary cement for any reason, try using a small amount of normal denture fixatives, or, alternatively, a little petroleum jelly. If you go this route, then try to avoid chewing with the area of your mouth that contains the damaged tooth because this could cause the grown to become dislodged again.