The reason behind your reaction is most likely histamine release.
IV Morphine releases a large amount of histamine & some people find this to be very unpleasant.
I personally find the histamine release of high dose morphine to be unpleasant myself.
As such the method that I & many others use to combat this is anti-histamine's.
I personally prefer Hydroxyzine or Promethazine but others use Diphenhydramine, etc.
Taking the anti-histamine before using the morphine will prevent or at least reduce histamine reaction.
As such you'll have a lot less "pins & needles", itching, burning, etc. than you would otherwise.
In some cases it may even prevent those effects completely.
Just keep in mind that anti-histamine's are also sedating especially some of the earlier ones.
As such you may need to adjust your dose accordingly.
Actually also keep in mind that some anti-histamine's are enzyme inhibitors & potentiate morphine.
Again you'll want to adjust you dosage accordingly as IMHO there's a noticeable increase in effects.
Hopefully that gives you some insight into what occurred & how to deal with it if you choose to do so again in the future.
Though it's not asked for in your question I'm going to throw in my obligatory warning.
If you liked it to much don't get started with it. You've probably heard it before but it's not worth it.
I'll let my preaching end there but as someone still dealing with opiate related issues going the IV route
only hastened the inevitable tolerance & withdrawal issues that eventually get most everyone.
Either way that ends my preaching & hopefully I've answered your question to your satisfaction.
I could go into more detail if need be but it seemed you weren't looking for anything to technical.
Just a general answer to explain the reason for why you experienced what you did.
I'm glad you enjoyed your experience & hope that the posted information is of use to you.
