This story has been floating around the net for the past day or so, but this report comes from a person who is in a position to know such things. As I know very well (having been gulled into wrongly announcing Khamenei’s death a while back), it is easy to be misled, and Khamenei has had previous medical emergencies in the past, and recovered, but the source is excellent. Nonetheless, it’s always smart to apply the Reagan Caution: Trust, but verify. I’m doing my best.
Here is what he/she says:
Yesterday afternoon at 2.15PM local time, Khamenei collapsed and
was taken to his special clinic. Nobody – except his son and the
doctors – has since been allowed to get near him.
His official, but secret, status is: “in the hands of the gods”.
Reportedly this collapse is natural. Many would like him to move to his
afterlife but reportedly the collapse was not ‘externally induced’
[no poisioning]. The few insiders who know about the collapse see
this development “as a gift from the gods”.
His condition had already seriously deteriorated over the last
months, aggravated by his nervous condition due to  his
inability to solve the problems created by his manipulation of the
election results and the refusal of [a large part of] the
population to accept this, plus  his loss of religious authority
by means of the repeated condemnations of events by senior clerics
Reportedly the principal aims of Khamenei of the last couple of
weeks, if not months, were to ensure  a positive reputation as
his legacy and  the physical survival of his family members and
their wealth, reportedly now largely in Syria and in Turkey (remember the truck convoy of $8.5 billion in cash and gold that was seized by the Turks?).
Outlook is uncertain but speculation is – considering that he is in
coma since more than 24 hours – that he may not come out of his coma and/or that he may die very soon.
If he dies it is expected that immediately a bloody clash will
develop between the powers behind Rafsanjani, who will immediately
claim temporary religious authority and overall control, and the
powers behind Achmadinejad who will scramble in order to regain
control and ensure their survival.
UPDATE (Wednesday Oct 14th): According to a bulletin from the Greens (Moussavi/Karroubi et al), there are widespread rumors in the Tehran Bazaar that Khamenei has died. The Greens say they cannot confirm it, but that there is an “abnormal atmosphere” in the streets, which almost certainly means there are more security people than usual.
The bazaar will apparently be closed tomorrow, and perhaps Friday as well, pending developments.