I'm not 100% sure so maybe I shouldn't even be touching this, but I'll give it a go.
Stricken, as I'm sure you know, is the past participle of "strike."
Strike can mean happen, occur, or to physically hit.
Struck is almost the same thing, as it's a past participle of strike, but it's more simple.
So really, stricken just sounds fancier. We have a lot of words in English that aren't used as much as they used to be, or only used to put more emphasis or make things sound more dramatic.
"Jeremy went outside during a lightning storm, and I swear to you, lightning came down from the sky and struck him dead." In the sense that it physically hit him.
"It struck me as somewhat unfair for Johnny to ignore his younger brother and ask the older boys to play." In the sense that it occurred to someone that Johnny wasn't really being fair.
It can also be used in this way: "The grieving mother was struck with awe as suddenly, out of the crowd, stepped her son who had been believed to be lost in battle!"
Now, as for stricken...Like I said, same thing. Only sounds fancier. It can mean to physically hit, or it can be more of an emotional thing.
In "Helen Keller was stricken blind and deaf," they're talking about something that happened to Helen. She could have been "struck with a terrible illness," but whoever wrote that line...chose to use stricken instead of struck. It's just really one of those words that just...is. There's probably an explanation buried deep inside some textbook somewhere, but, yeah...I don't know it.
Sorry. I probably just confused you even more. Someone will come along soon, I'm sure, and elaborate. Sorry I couldn't be of more help.