Coins are uniform in size. Last but not least, if you have pets, be sure to note any unusual behavior they are exhibiting. Be on the alert for them oversleeping or seeming to be disorientated or drowsey. Note the time and date. This may coincide with your abduction as anxiety in the animal may.
Fish seem prone to anxiety verses drowsiness.
This will allow you to rule out any outside interactions that may be interferring with your sleep or awareness.