While searching some more, I found an excellent resource on ancient Greek (although website is a bit slow and sometimes it throws exceptions). The word describing a state of blindness inflicted by the gods was known as θεοβλαβεία (infatuation sent by the gods, madness, blindness).
I still can't find the specific source where I first saw it, but I could find it in quite a few other texts, many of them matching very well, e.g.
Appian, the Civil Wars, chapter X (greek, english) :
Although he had been on his guard against them at Dyrrachium, a certain spell seems to have come over him at a time when it would inure most to Cæsar's advantage. Under this spell also Pompey's army was most nonsensically puffed up, and rendered insubordinate to its own commander, and hurried into action without previous experience in war. But this was the ordering of divine Providence to bring in the imperial power which now embraces everything.
Appian, Syrian Wars, chapter VI (greek, english)
Yet he was so beside himself that he did not even defend the crossing, but hastened to reach the interior in advance of the enemy, not even leaving a guard at the straits.
In this particular text, this expression appeared also in another form:
ὑπὸ δὴ τῶνδε πάντων ἐκταρασσόμενός τε, καὶ θεοῦ βλάπτοντος ἤδη τοὺς λογισμούς, ὅπερ ἅπασι προσιόντων ἀτυχημάτων ἐπιγίγνεται (...)
Translated as (same source):
Everything unnerved him, and the deity took away his reasoning powers (as is usually the case when misfortunes multiply)
However, even though this is the exact word I was looking for, I feel that ἄτη actually expresses better the state I was asking about in question. This is especially true if put in context, why I started searching for the word in the first place. That's why I will accept the other answer (and I wish I could accept two, since they are really close).