In the case of dermal anchors/single-point piercings/implants, you lose virtually 1% of the piercing, namely the anchor’s upper attachment, or the dermal piercing’s anchor disc.
The lower portion of the piercing is still in the skin, whereas the upper attachment (the round disc) can fall out.
That means that, while you may not feel or see the lower portion, 99% of it is still under your skin.
If you can refind the upper disc quickly, you can try and re-attach it.
Note, however, that you will not be able to get it back on as tight as in the piercing studio, therefore you should ALWAYS go to your studio and have it reattached properly.
If you are not able to reattach it, don’t worry. Even if a small piece of skin begins to grow over it, that does not pose a problem.
There is no danger that the anchor beneath the skin will move or fall out, so don’t be concerned. That said, you should still visit your piercing studio as soon as you can.
In the meantime, cover the area with a band-aid.
-> A dermal anchor should not be worn for long without an anchor disc, because a layer of skin will end up growing over the anchor. Although a single surface piercing will not slide out or move to a great extent, it can be slightly twisted from its original position or be shifted askew.
This should be avoided, because if a layer of skin does end up growing over it, it can be painful to remove it, and if the anchor beneath has moved slightly, it can be readjusted, but this too can be unpleasant.
In short, if you happen to lose your dermal anchor/single surface piercing’s disc, you should go to a piercing studio as soon as possible, and in the meantime screw on a replacement disc in order to deal with the risks outlined above.