Dealing with past regret

[losin]

How do I deal with past regrets? I am often struck with a thought in the middle of the night about something I should have done in the past.
This happened at 4am this morning. It suddenly hit me that something I hadn't done meant we missed out on a lot of money in the past. I genuinely hadn't realised until this morning and I have no idea why I think of or remember these things out of the blue (I guess that is ocd working at its best - suddenly finding a thought to scare the hell out of you).
Against my better judgement I asked my husband about it and he just shrugged and said 'ah well, we didn't miss the money at the time and it's too late to do anything about it now - just let it go'.
I want to do just that, let it go and leave this thought in the past where it belongs but I really don't know how.
How do others deal with thoughts like this?

[BlueIris]

Mindfulness can really help with intrusive thoughts.

Yesterday I was hit by a really nasty health anxiety panic attack at 1am, but I was able to get myself back to sleep with mindful breathing. There are some really great guides available, but basically it amounts to focusing on your breathing and gently nudging your thoughts back to it every time they go in an unhelpful direction.

Sorry you're having such a rough time right now.

[losin]

So I'm giving the thought too much importance like my husband says? I feel I should be worrying about this as it's something we lost out on. Does it really not matter as it's in the past and I can't change it? It seems such an important thing right now 😢

[BlueIris]

It's not something you can do anything about, so there really isn't any point in getting upset about it.

[losin]

That's what my husband says but I feel so angry with myself and so stupid for making such a ridiculous mistake. I'm not good with facts figures and paperwork in general which is how I made the mistake in the first place. I need to find aome way to convince myself it doesn't matter and to let it go, but right now I hate myself so much!