Give that a read because it's interesting, if you want, but here's the rundown of what it means for Fabian:
It knocked him unconscious on site and blew his shoes right off (his feet were burned too)
He got the cool tree branch shaped scar all up his right arm (because he was brandishing the sword and the electricity entered through his hand)
His brain was a bit affected with a little bit of memory loss (not TOTAL LOSS, but foggy, distant details) that will be relevant to: -- Emmeline (Fay will lose a little bit of the trauma over seeing the state Em was in when she came back, the whole week of looking for her, and some of his guilt around her getting taken in the first place) -- Anton (Fay will forget some of the details of the benefit night, including noticing Anton leave before the DE attack, but he will remember the more recent stuff from when he was over after Em was back and Anton fed him and they talked, so suspicions not TOTALLY gone, but less)
He will also have a bit of personality change in that he'll be a little less confrontational maybe, a little more YOLO (which he was already pretty YOLO, so... watch out world, lol)
A New Skill! Sometimes lightning strikes give people nifty new talents, so a little better at wandless/wordless magic now. This is def NOT Dumbledore level skill boost, and does not make fay a Special Snowflake Badass. Just a minor level up. He will still use his wand for most things, just more instinctive stuff (combat and shield spells, for example) will come easier without a wand.
So the changes will be subtle-ish, maybe at first chalked up to him being a little addled by the lightning and expecting it to go away. Just FYI for those who are close enough to Fay to notice these sorts of changes!