Worried about potential injury

This question, unfortunately, comes up occasionally on our site.  The short answser is you are nearly guaranteed to be fine minus some localized bruising.  Before I give a slightly longer answer, I will preface it with the best person to ask is the practitioner that you saw.  They will know exactly which points they needled, which length and guage of needles they used, and will be better positioned to offer informed feedback.

The slightly longer answer is that unless the needle used was long and/or you are fairly thin there is little to no chance of the needle causing internal damage.  Acupuncture needles are extremely thin and simply not that strong, so in most cases they will bend once they hit anything that restricts their movement unless they are being guided through those areas skillfully.  Further, outside of incredibly rare occurrences there are only two potential issues with acupuncture - one is lung punctures (very rare, generally known fairly soon after needling/treatment) and the other is nerve damage from improper needling technique (also fairly rare and also know fairly soon after needling/treatment if not immediately).  Even those two items heal in the vast majority of cases, so long-term damage from an acupuncture treatment even in the worst of circumstances is extremely, extremely rare.  

I'm assuming the needle was left in at CV 6 - so in the scheme of things if you were going to find a needle later that's probably one of the safest places to find one.  This should, of course, never happen.  Most acupuncturists keep very strong records of each point they used, count the needles going in and coming out, etc. to avoid this from happening.  But it does happen, albeit rarely.  I would imagine many acupuncturists have at least once left a needle in a patient.  They may not have got all the way out of the office with one in them, but they at least got to the reception desk.

I'm fairly sure you will be fine, but I would speak with your practitioner.  Also it would be good to hear their response before you consider further treatments from them.