UPDATE: The issue seems to have been resolved.
Worried that you may have lost all your Twitter followers? You're not alone!
It looks like Twitter's follower count has gone down and been reset to zero. This has happened several times before--most recently, less than a month ago.
There's currently no mention of the error on Twitter's status blog, but Twitter users are reporting the glitch:
mindofmo: @Twitter: It is PROFOUNDLY unsettling when hard-hard-hard-won Follower count disappears, with never an explanation. Put self at my keyboard.
A_moreee: This whole twitter momentarily resetting my follower/following count is getting old, leave it at zero for all I care, just show me ze goods.
malthejepsen: Lulz... Twitter just reset everyone's follower count
NobueIto: So why does this follower/following count glitch keep coming back? You'd think Twitter would have a handle on it by now.