How fast and logical can you think in a critical situation?

So, this happened to me today and I can't express how it made me feel, because I felt a handful of emotions.
I was at work and there is a guy coming in, saying he needs a 50lv bill and he gives me change of 50. I say ok and carefully count the money, because the guys looks like a gypsy and talks like one (alright, he was a gypsy and I was being prejudicial). The money were 50 indeed, so I just found a bill of 50 and gave it to him, holding on to the money he gave me. So, then, I just blinked and realized he was holding a 10lv bill and he said "But I didn't want change, I want to make only 1 bill out of them, just one 50".

 I was shocked. I was shocked at first because of the first statement "I have just made a mistake". Then, I was shocked again, but for a different reason "Did I really gave him 10lv-bill instead of 50lv-bill?" And then again, I felt stressed because of the thought "Omg! Now I'm not sure if I was thinking about the 50-bill or I really gave him such!" Confused, my thoughts were running really fast.
"Am I judging him just because he is a gypsy? Am I trying to defend my mistake,  thinking of the possibility that since he's a gypsy, he's trying to trick me? Am I so stupid to really give him 10lv-bill instead of 50? Am I so stupid to fall victim to this eventual trick?
- I gave you a 50! - I said.
He acted surprised, looking at the 10 in his hand.
- You just gave me this? - saying in a call, confused voice.
- No, no! I just gave you 50! - I looked at my co-workers, which were 3 of them. - Does anyone knows what kind of bills we had here? I need to know did we had any 10s in here?
My co-workers were confused, neither of them could be sure what kind were the bills, neither did I. But I made one of my co-workers to squeeze to the change of 50 he gave me and she advised me to check in the document we write the balance, and it clearly showed that I have given 50 after all.
He started showing his pockets in order to prove he doesn't have any other money on him, but I already started to get angry. Angry that he is actually trying to cheat and make me give him a 50 one more time. Secondly started to get angry that for a second I doubted myself and my own concentration. I was so pissed of his cheap prank. BUT! At the very same second I was also afraid that maybe, because of some slight chance, the balance-document wasn't up to date and maybe I'm wrong after all. Yes, I was stressed that maybe I can be wrong after all and believe me, If you are talking to 3-times-bigger-than-you-gypsy-guy saying he is lying to you, you will be a little afraid of him too. So, I was now really carefully investigating how he will act when I say "No, you are lying!". I clearly knew, that this is a critical moment of my "fight". All depended on this moment - bluffing (even if just a little) that I'm absolutely sure that I gave him the 50. I had to look and sound and act as 120% sure I'm right. But you know what guys? I was still not 100% sure in that. But his acting now would tell me the answer. Just imagine yourself giving a change of 50 in a shop and they give you just 10 back and saying you lie. Would you look calm, not shouting and cursing? No. Well, he kind of did. And then I made my final conclusion I am indeed right and I was ready to beat him up if he doesn't disappear of my store! I think he felt my deadly aura and gave up on this prank. Maybe just because it was 4 of us, or maybe just because I am certainly not the type of person you can trick.

And in the end I realized how lucky was really I. How lucky that the balance at that moment was a small number and counting it wasn't waking longer than 10 seconds. Believe me, sometimes counting may take up to 10 min. In the state I was, I doubt I could count right, influenced by that. Also, I was lucky my co-workers were all there. Even if not saying much, they made me feel the power of authority, the power of a dominant creature. They were my pack, I was the alpha and I was lucky to feel this way, because it gave me confidence and I felt as I'm not alone in my decision, in my statement.

So, in the end I felt shock, distress, fear, doubt, anger, relief and gladness in the short time of 1 minute. Maybe it didn't take even that long. Thank you, God, thank you, my co-workers, thank ME, for that I'm always on the alert, even just unconsciously. Thank ME, that I keep one on mind in everything I do, even If I don't realize I'm paying any attention at the things I do.