This is a common phrase uttered by collectors of novice to well-seasoned
reputation and is a natural occurence that happens to everyone.
There could be multiple reasons you are not feeling your spirits and the chance that they have left you, abandoned you or otherwise dissipated is less than 1%. To start with spirits can NOT leave a vessel or soul once they are bound. From here on the word "vessel" will encompass both a physical object and/or being bound to a human's spirit.
Spirits do not have free will to change vessel or abandon a vessel at whim. They are eager to be given a home and find it as their personal sanctuary and safe haven. They are not going to up and abandon their shelter and more than you would abandon your home. They cannot leave their vessels to go to other people or other places. While it is possible they can be sent on errand for you to help another person they cannot make that decision by themselves. If you ask them to give aid, comfort or other assistance to a friend, family member or stranger and they have the ability to do so then you may feel a temporary absence during their time helping the person you specified but they cannot decide to take leave of you by themselves.
The odds that someone powerful enough and with enough skill will choose to steal your spirit(s) from their vessels is less than a 1% chance. Any reputable conjurer will bind the spirit with a protection invocation as part of the binding process limiting drastically the chances that the spirit can be unwillingly removed from their vessel.
The reasons you may not be feeling your spirit(s) could be a change in your energy... a drastic swing from happy to sad, taking medicine, changing dosages of medicine, or on the more unpleasant side having a hex, curse or evil eye placed upon you.
If that is the case the removal of said hex, curse, etc will allow your spirits to contact you again and that can take anywhere from 24-96 hours after it is removed. There are ways to protect yourself by owning at least one entity for protection, though multiple entities are recommended.
However the simplest reason, and most common, is just a change of energy. Perhaps you're not getting as much sleep as you used to, you have had a life change (new job, newborn, moved somewhere new, breakup, divorce, etc), drastic change in diet, and these are temporary energy changes that will straighten themselves out.
It could also be that you are not a naturally sensitive person and have a more difficult time achieving contact with the paranormal.
So don't worry! With patience, focus and determination to try your best you will find yourself in contact.