What advice do you have for managing irrational thoughts and feelings?

Let them run their course, really.

The easiest way to get over irrational insecurities and intrusive thoughts is to face them head on. Trying to stop thinking about them usually only makes it worse. Think them out. Write it down, if that helps. Frankly, I find writing this stuff down to be exceptionally helpful, for me. Play it out in your head to the absolute worst case scenario, the most irrational, dramatic outcomes that you can possibly think of as a result of what might happen if your fear comes true.
Then decide which parts of it are within your control, and figure out and implement whatever you might need to do to change those things to make yourself feel more secure. Then figure out what things you have no control over, and let them go. Recognize that some things are out of your control and worrying about them will not change the outcome. Then sit back and really look at what you’ve discovered while picking things apart, and you might have just enough clarity to let it go.

Best advice I can give, most of the time the things you fear will happen or are happening behind the scenes don’t. As far as being angry about the past events, you have to work on learning to let go. Meditation is a good tool.

My stock (and annoying) answer = start a meditation practice.

In addition, make sure you point out to your friend that venting about this stuff is not helping her.

First, have your feelings fully. Ignore the fact that you think they are irrational. Give in to them and experience them.

Then write about them. Put aside thought and just write about what you are feeling. Ask yourself why you are feeling that way. Then write whatever comes into your head. Don’t filter it.

You may get some information on a similar situation that you experienced in childhood that this current experience is echoing.

In the short term, very little you can do. In the long term, a little time after each incident, analyze why its happening. Think it through. Once you do that, you can come up with a strategy for slowly working these things out of your system.

That being said, irrational is not the same as hard to explain. Don’t close off the possibility that these “irrational thoughts” are really just “instincts” and that they may mean something (unless you have evidence that you often have these thoughts and are wrong).

You don’t “manage” irrational thought.
Attempting to manage thought feeds it energy.

It’s like trying to wash blood away with blood.
Ain’t gonna work.

Best to simply observe thought.
It’ll eventually dissipate through lack of (new) energy.

Punch a punching bag. Hard.

You live, you learn. Face them, experience them and then look back and see what you did right or wrong. You can’t reason away irrationality, but you can learn to live with it, even ignore it.

In addition to observing as mentioned above, once you are satisfied that the feelings are not justified (maybe justified/not justified is better criteria) then you should act the opposite and commit to your action 100%. This is a CBT technique.

The best way to fight bad thoughts is to not fight them. When you start to think about them, let them flow across your brain, uninterrupted. It’s when you try to struggle with them, then it gets obsessive and it becomes disturbing. It’s your mind playing tricks. Let it do its tricks. A good reference to dealing with this problem is one of the self-help books by Dr. Clare Weekes, like “Hope and Help For Your Nerves”. You can Google it or look for it in the library.

I deal with it by knowing it will pass, by letting it wash over me but by being sure that I’ve been here before and it got better. Certain anxieties though, at the pit of my stomach, are my body’s was of telling me something isn’t right, to watch out, esp. in relationships. And I consider myself to be a very logical person, yet I don’t think this kind of sensing things is illogical.

Irrational insecurities have to do with feelings and it is worth examining your feelings. If the relationship is sound and solid then the insecurities lie within yourself and not elsewhere. These insecurities may arise from a divided mind that wants the relationship and yet doesn’t want it. This conflict gives rise to stress and a sense that things are not going to last.

Consider the negative points in the relationship. Think hard about them and write them down. What don’t you like about the relationship? It what ways does it cramp your style? Now see if there are ways that these negative points can be overcome within the relationship. Can you discuss any of this with the other person?

If you were asking about yourself, I would say have a complete medical check up to rule out any hormonal cause. When my thyroid malfunction gets out of balance, I have feelings like you describe.

Since it is your friend, maybe you could somehow suggest seeing a doctor.

Learning to benefit from the techniques of Cognitive Behaviour Therapy is best learn from a professional (psychologist or psychiatrist) in person over a short series of sessions. The learning will provide a lasting benefit.