I have experienced this plenty of times. When this happens to me it usually makes me have a panic attack. I notice that I experience this when I am under a lot of stress. The last time this has happened to me was a couple of days ago when I was laying down. I thought that I was going to have a panic attack but I got up and started cleaning and I forgot about it. This year has been the worst year for my anxiety and panic attacks. I lost count of how many times I've had a panic attack. So, I have experience alot of the weird side effects that anxiety can cause such feeling like passing out, brain fog, heart palpitations, pressure in head, neck and head pain, adrenaline rushes out of nowhere, chest pain, stomach issues and dissociating. I find that being active and drinking enough water helps. When I feel really stressed I take magnesium citrate and it calms me down. I also realized that I wasn't breathing properly, so I started doing breathing exercises and I have seen an improvement.