The undescribable feeling near the finish line when (for me) you had been on the move for 4+hours, had been thinking about the sacrifices for you and your family, the training, etc. For thr last mile or so I was thinking about it all and was nearly in tears (and I *never* cry - dead relatives, divorces, the lot).
Don't get me wrong, I'm glad I did it - as a personal challenge (I didn't do it for charity), but I'm glad I've done it and can move on to something (or nothing) else now.
Please don't let me put you off. Something like this is, I think, something everyone should do at some time in their life. Get out of the comfort zone.
To be honest I have been tempted to do it again - because the time I did wasn't close to what I wanted to do. Sadly since then I've rediscovered food, beer, gin etc so it's still just a dream.