Vulnerability is an experience of feeling exposed, accessible, hurt-able, noticeable, visible, targeted and attacked. When you are vulnerable you perceive that the whole world is out to get you.
Experiencing vulnerability is a familiar state that you normally refer to as "afraid". It's another word for it. You can't help but experience what you call 'fear' when you are seeing yourself as being attackable.
However, this sense of being vulnerable has only come about because you have created an enemy within your own mind. You've projected this enemy onto other people or situations, thinking they now are the cause of the threat, but the enemy is still in your own mind. And since you created it, you can undo it.
It is therefore possible to stop feeling vulnerable, and to re-access a state of INVULNERABILITY.
Any form of resistance will create a division in your mind, a separation, and will make your mind be "split". Literally, your mind seems to take on two identities, one which experiences itself as being victimized, and the other which experiences itself as being a victimizer.
Usually the part that is a victim uses denial and disassociation to block awareness that the victimizer part is also a part of the same mind. It is the victim's resistance to the victimizer that makes it a victim in the first place, and denies and therefore projects the victimizer into being. The victim then does not perceive that they themselves are the cause of their own victimization, that they are literally doing it to themselves within their own mind, that their mind is in a state of self-attack, and that they therefore could do something to stop it.
A sense of vulnerability must occur as soon as you have made yourself unwhole. This can happen in many forms including self-abandonment, self-attack, self-rejection, denial, believing in enemies, resistance to the truth, trying to block awareness, blame, scapegoating, trying to stop things from happening, being controlling, not accepting everything as it is, etc. These are all forms of separating and putting up walls. And putting up walls, experientially, actually takes down walls in your mind, producing an experiencing of having become exposed to something that you were previously safe from.
You can't feel safe while you are attacking yourself.
What you can realize though, is that it is YOU that is attacking yourself, and it has nothing to do with anyone else. Immediately you will feel significant reduction in the experience of exposure and vulnerability, if you can remind yourself that you are not being affected by other people or situations. They are NOT the cause. That alone will relieve much of your anxiety. This also deflates some of your belief in separation and your resistance to yourself. But you need to take it further and undo as much as you can of the split that's happened inside your own self.
Quite literally, you can become completely invulnerable. Or rather, recognize that your invulnerability is still completely intact and was simply blocked from your awareness when you thought you were vulnerable. You can become whole, free of the split mind of the ego, and experiencing your SELF as free of attack. In such a state, there is nothing outside of you which can bring about an internal experience of attack, and therefore you are invulnerable to everything. Nobody can give it to you or take it away. If you do not choose to believe in attack, you will have no enemies. And then you will enjoy peace of mind.