CreatureEvent What the hell is going on?!

[Mitsuri]

I want one doll to drain health points from the enemy.

Firstly I did it as follows:

function drainHP(cid, target)
-- GET HEALTH
local CreatureHealth = getCreatureHealth(target)
if (CreatureHealth < 10000) then
if (isPlayer(target)) then
healthToAdd = math.random(CreatureHealth/15, CreatureHealth/13)
else
healthToAdd = math.random(CreatureHealth/12, CreatureHealth/10)
end

roundHealth = math.ceil(healthToAdd)
doCreatureAddHealth(cid, roundHealth)
doCreatureAddHealth(cid, -roundHealth)
end

addEvent(drainHP, 2000, cid, target)
end

function onAttack(cid, target)
if (getPlayerStorageValue(cid, 25000) > -1) then
addEvent(drainHP, 2000, cid, target)
else
stopEvent(drainHP)
end
return TRUE
end

but it went crazy, even when I wasn't attacking monster (but I had it selected) physically I was receiving health twice a second ! ! !

Then I wanted to check out what the hell is going on by:

function drainHP(cid, target)
-- GET HEALTH
local CreatureHealth = getCreatureHealth(target)
doPlayerSendTextMessage(cid, 25, getCreatureName(target) .. ':' ..CreatureHealth)

addEvent(drainHP, 2000, cid, target, minuteStack)
end

function onAttack(cid, target)
if (getPlayerStorageValue(cid, 25000) > -1) then
addEvent(drainHP, 2000, cid, target)
else
stopEvent(drainHP)
end
return TRUE
end

but it was same as above!

Then I did something like this:

function drainHP(cid, target, stack)
-- GET HEALTH
local minuteStack = stack

if (minuteStack == 10) then
local CreatureHealth = getCreatureHealth(target)
doPlayerSendTextMessage(cid, 25, getCreatureName(target) .. ':' ..CreatureHealth)
minuteStack = 0
else
minuteStack = (minuteStack + 1)
end
addEvent(drainHP, 2000, cid, target, minuteStack)
end

function onAttack(cid, target)
local minuteStack = 0
if (getPlayerStorageValue(cid, 25000) > -1) then
addEvent(drainHP, 2000, cid, target, minuteStack)
else
stopEvent(drainHP)
end
return TRUE
end

But it went even worse! Even after stopping (de-selecting) monster I was reciving info about his health points! Twice a second!

Can someone tell me what the hell is going on with this script ?!