i know how u feel mate!! , i lost what I'm sure was a massive brown while fishing Harelaw while on the Pollock shore at the far end in a small bay,, and my leader was 8lb with 6lb droppers of which it was the middle dropper in which it had hooked up on ,which was a Bibio in-case you are interested ,,and what made me think it was a big brown was the definite buttery yellow flash i got when i had the fish at about 10-15 yards when it steamed of at high speed and got its nose down .
i had only fished Harelaw a few times and did not realize it had some big rocks in it and while playing the fish he made a sudden dive and a turn to the right in which i reacted to by adding side strain on him/her ,but just as i though i was about to turn him and get a chance to see him again,, he made one last surge ,,and the ghastly desperate lack of tension on the line was evident as i desperately tried to gain line in the hope i had misjudged the run of the fish while all the time praying he/she was still hooked .
i am sure i will get another shot at a big fish on Harelaw or some other fishery as I'm sure you will too ,so keep your head up and try to use it as a learning curb as i can assure you it will all come flashing back the next time you get a big fish on and the mistakes you made will be so clear like the have never been until the very moment , and this i believe is when we learn our real forward steps in our angling ,so good luck and keep fishing ,,i only wish i was as brave to be out in that bitter cold fishing .