Does any of the early church fathers teach that we as Christians are allowed to defend ourselves if our life is in severe danger and if so what church fathers taught this?
There is an excellent article by Henry J. Cadbury: The Basis of Early Christian Antimilitarism
In there he does rather thorough analysis of the writings on the early Christians on the concept and necessity of warfare, and he also goes on a small side trip on self-defense, too:
That the early Christians did not construe non-resistance as a purely negative and passive virtue is also evident from many passages. "'It is not limited,'" says Lactantius, "'to this-that (a man) should not inflict injury, but that he should not avenge it when inflicted on himself.'" Indeed, it is not limited to refraining from revenge but expresses itself in deeds of active love, repaying in kindness. It means, Athenagoras explains, for men "instead of speaking ill of those who have reviled them- to abstain from which is, of itself, an evidence of no mean forbearance-to bless them and to pray for those who plot against their lives." The Christian, says Lactantius, "must diligently take care lest by any fault of his he should at any time make an enemy."
However, article points out that there were soldiers among Early Christians, so it can't be said they all were pacifists, and preferred flight to fight. But this was part of the doctrine to offer no resistance and numerous writers pointed out that this was the best way to profess their faith and, subsequently, was the most sucessfull way for Christianity to thrive:
"For religion is to be defended, not by putting to death, but by dying; not by cruelty, but by patient endurance; not by guilt, but by good faith; for the former belong to evils, but the latter to goods; and it is necessary for that which is good to have place in religion, and not that which is evil. For if you wish to defend religion by bloodshed, and by tortures, and by guilt, it will no longer be defended, but will be polluted and profaned. For nothing is so much a matter of free will as religion." - writes Lactantius,
"The adversary (persecution, or the persecutor) had leapt forth to disturb the camp of Christ with violent terror . . but he perceived that the soldiers of Christ are now watching, and stand sober and armed for the battle; that they cannot be conquered, but that they can die; and that by this very fact they are invincible, that they do not fear death; that they do not in turn assail their assailants, since it is not lawful for the innocent even to kill the guilty; but they readily deliver up both their lives and their blood." - said Cyprian, and Origen seconds:
"Since it was the purpose of God that the nations should receive the benefits of Christ's teaching, all the devices of men against Christians have been brought to nought; for the more that kings and rulers and peoples have persecuted them everywhere the more have they increased in number and grown in strength."
It needs to be pointed out, though, that early Christians were living largely peacefully, with only occasional periods of persecution, and rarely it was widespread. Nevertheless, it was not common for Christians to resort to martyrdom, so most often what happened was either flight or accepting the requirements of the persecutors, even though most of the Church members were aware they are more than adequately numerous to offer successful armed resistance.
Catholic Church in Canons 2263-2267 on Legitimate Defense reconciles those views with all the other places where Scripture references use of arms and self defense, but those are, obviously, not the real answer to this question.