I think it's debatable whether or not the same standard applies to speaking in tongues, and I am very wary of people who claim that God has compelled them to do something that directly damages their bodies, BUT -- if we're going to accept Daniel (and if we don't accept Daniel, we might as well not accept any of the Bible), then we must conclude that stress, faintness, incapacitation, or even being driven to bed for days does not neccessarily mean that the said activity is not of God, neither does it say, even, that the person who participated in it is under attack.
heh...not that you can serve God and not be under attack...
It is, however, something to pray about, and to seek understanding on. Whether you are under attack or whether you are just faint, 1) don't be discouraged, and 2) pray that God strengthens you, because (given that these tongues are of God) if you become faint now, just think about how it will be when you begin to come to things that bring understanding.
Still, I think it would also be best to search yourself and the Holy Spirit to be sure that everything is right--in you, in the tongues, and in everything else. Come to a good conclusion, and then don't sweat it.