Hi Nacho:
What you are describing sounds to me like you may have picked up a stray bit of negative energy from someone (possibly non-physical) that may have been in the vicinity of your healing (not necessarily in the same room at exactly the same time - because I'm sure Master Lin would have recognized that). When you are receiving energy healings, sometimes you are still very "open" for quite some time coming out of those sessions.
My suggestion to you would be to remain calm, refuse to entertain negative thoughts concerning your abilities (2 years of Qigong has probably taught you much!), and provide yourself with strong positive affirmations while doing some lighter Qigong exercise and meditation. Also, consider that the cold-sore is just energy, like everything else - so at this stage of your training, it shouldn't be a huge step to figure out how to draw the energy off of it.
I'm thinking also that IF you've had anything that has been a shock to your system lately, this could be contributing to your anxiety. If you have the Anxiety paraliminal, use it.
Please keep us posted so we can help you through this.
Cheers!
Unis 
