Some people with PTSD experience dissociation and depersonalization symptoms. It usually happens after being triggered by something that reminds them of the trauma, during a panic attack, spontaneously as a result of constant high anxiety stress levels or when they find their minds circling over and over again about thoughts of the trauma.
Grounding techniques are a great way to help stay present in the here and now.
There are different ways to stay grounded. A couple of the best ways are:
1) List five things in your head that you can see, five things you can feel and five things you can hear.
2) Tap on a part of your body (wrist, leg, arm).