Hi James and all others who entered into this discussion.
I have had the same experience with Urticaria and, considering it has happened on several retreats at different centres and that nothing (diet or environment) could be attributed, it is, I have concluded, the result of rising Sankaras. I could be completely wrong on this but symptoms and 'stuff' arising seem to always correlate. And yes, continuing to meditate seems to be the best form of defense, IF you are in a position to do so.
Currently I am in East Timor self-funding several projects with the more vulnerable, of which there are plenty. ET is a difficult country and many opportunities for falling back on compassion are indeed made available to you. The problem is I attempted to meditate last night for a mere 15minutes (I admit I fell asleep sitting up and had to retire) but awoke half through the night with Urticaria on my neck and chest. Despite them showing no indication of working in the past, I've opted to take antihistamines on the off-chance this has been triggered by an allergic reaction but, from previous experience, all indications are that it is most definitely NOT. I actually joined this site looking for answers and yours was the only post I came across.
Attending vital meetings, conducting lengthy training sessions on depleted energy and dealing with the heat, dust and on-going stresses the 'dynamic' Timorese culture offers up, the last thing I need is this terribly distracting and, visually, embarrassing rash. And I know from experience that working through whatever has brought it up is, of course, the best approach....only NOT RIGHT NOW. So my choice for now is to 'sit on my sankaras', do my six very intense weeks in Dili, and deal with the underlying issues when I return to Australia. The downside of this being I CAN'T MEDITATE WITHOUT THIS CONDITION ARISING AND I WANT TO!!!!! Lets face it if just 15 weary minutes can bring such a condition on..oh dear. So James I can fully empathise.
Yeah Chickweed cream could be effective. I use what I have on hand here (Papaya Ointment) which seems to at least ease the itching if not the physical symptoms. Considering several doctors have confessed to me that modern medicine still doesn't fully understand the condition, you would have to land an extremely dedicated one for 'a visit to the doctor' to be of any particular use. However Ayurvedic medicine talks of such conditions arising from excess pitta so that may be worth some research. If, like myself, you are devoted to continuing your practice this may be of some help. Also on one retreat I attended at Blackheath I applied chamomile tea and that was particularly soothing. It's not that I have concern for the condition arising as a physical symptom of arising 'stuff'.....just not right now...
All the Best from Timor-Leste