Very stressed at moment, felt this heat come over me and passed out? could this be anxiety?

Possibly: Your symptoms could certainly be related to acute, severe anxiety. U nfortunately they could also be due to a variety of other, possibly more sinister symptoms including cardiac, endocrine or neurologic issues. It would be important to bring this up with your doctor.

Perhaps: Anxiety is not only common, but can cause many different manifestations. As a practicing dentist (orthodontist), i occasionally have seen patients who are so anxious (phobic) that they may have an episode of something called vaso-vagal syncope, a hot flash, dizziness and passing out can occur. Usually laying patient down will bring them around. So, yes it can.