I don't have much knowledge with this condition, perhaps others will come to your aid, I hope so. About a week after I had my 5 stents inserted, I suffered this and it did scare me until I realised what it was. I panicked the first time because I suffered a bad episode of arrythmia after my procedure and I thought it was happening again. Mine too came on late in the day, any time from 6pm onwards and lasted ages. The only way I managed to stop them was to have a sleep. Strange thing is, they stopped after a couple of weeks, they vanished as suddenly as they started. I only had one a day and I really have sympothy for those who suffer with it. I even thought I had trapped wind and forced myself to burp several times but this had no effect. Coughing, jumping up and down, running on the spot, holding my breath for a minute, nothing I tried stopped the flamin thing, only sleep. Why a short nap of 30-60 minutes would stop it I don't know.
When I lay down or even when it is time to sit and "relax" at night.
When you say at night, is this in particular when you lay down, especially on your left side?