I think the negative emotional experiences are easier to recall then a positive emotional experience that would qualify as a positive UDIN, certainly will be more aware now if that happens.  
The best example I can give for now is when I have a first session with new therapy clients; I already have had a phone consult, so they are on board with my approach to therapy and I feel I can help with their presenting issues, etc.  Though I usually am very particular and do not take on clients that I get a strong negative gut feeling about, sometimes I have a little bit of an uncertain feeling. 
I always feel a little nervous before first sessions, but with the ones with an uncertain feeling, there is an initial sense of nervousness, increased heart rate, little sensation in the stomach, a dread feeling anticipating that my gut feeling may be confirmed,...
I can remember one in particular a few months ago, felt that same way initially-- this was a referral of a friend of one of my current clients who had made one brief comment in particular after my initial phone consult that got me a bit concerned and I felt uncertain what I was getting into...The first session, we got talking (online) and I was just being myself and building rapport as I always do, the client was very engaged and presented differently then what I was expecting or concerned about, we had some laughs, overall went very well and the client and I both felt good about continuing to work together.  Whatever I initially felt was gone.
Of course this is a familiar feeling in general with meeting new clients connected to my evaluation of myself; when it is paired with a gut feeling that this client may not be a good case for me, more than I want to take on, it's connected to not feeling safe, not wanting to be burdened/responsible with something heavy, not in alignment with my values/goals for my current approach to my work/type of clients to work with...