Though this may appear to be my answer to everything lately, it may be because it's my answer to many of my own issues - you may want to look into food sensitivities. If you're allergic or intolerant of foods or classes of food chemicals, they can cause central nervous system stimulation and tachycardia (rapid heart rate). It also causes histamine release, which is a neurotransmitter implicated in anxious feelings. I have found a direct correlation to eating something to which I'm intolerant (which, unfortunately, could be one of multitudinous things) and having flushing and anxiousness - and having no control over it. When I'm toxin-free, these feelings don't happen (some latent fear that it will happen is always there - but then I'm pleasantly surprised when I speak to someone and my heart rate doesn't go up and I feel quite at ease). While I've gotten good at cognitive behavioral therapy techniques, mindfulness meditation, hardcore do-or-die willpower and what-have-you I've found that food intolerance was always the root problem. My first improvement was getting rid of gut dysbiosis because yeast is one of my many triggers, and I most certainly had fungal overgrowth in my early twenties when these symptoms were at their worst. (If you happen to have dysbiosis, just be careful that you don't treat it with "food remedies" to which you may also have sensitivities, as was the case for me.)
This is something of a wild guess here, but ever since I've pinpointed this in myself I've suspected that many people with social anxiety are at the mercy of their overly-amped nervous system in constant flight or flight mode caused by food chemicals. My previous degree is in psychology so there can be any number of potential reasons for social anxiety or phobia however I have a strong hunch that food is at least a potentiating factor, even if there is significant genetic/epigenetic hardwiring at work as well.