They aren't, imo, but what happens is your player goes cold, which can/does modify his performance negatively (especially if they are more average/borderline players or at least in weaker/borderline skills), which then makes it more likely for the player to struggle, which keeps him cold, and so on.
Of course, the reverse is true for hot. A hot player that's also talented can be near unstoppable. Still remember the year Wil Myers was having before I switched - 37-game hitting streak, batting over .400 into May with power - totally insane. Same with Longoria the year before - hit like .360 with 40+ HR.
That might lend to a scripted feel, but a few games of bad luck can send the player spiraling down for a while - just like smacking 2 HR and going 7-for-12 in a series can fire him right up.
I do think they are more volatile this year. Last year, it seems more regulated on the "last 10 games". This year, I've seen more game-by-game changes than I remember seeing last year.