Yes, absolutely.

Your subconscious cannot really tell the difference between your imagination and memories of actual events, so yes, you can traumatize yourself.

If anything it can be worse than a real break-up, because in the real world you come to know the other person's faults and flaws, you know how the relationship could at times be a chore and so on. If it's just your imagination then he or she was perfect, the relationship was all roses and there's no actual closure. Nothing actually happened to end the relationship, so you're left with a dangling short-circuit.

I gave some advice to someone the other day on here, for a technique that can work wonders in this situation, lemme find it.. Here ya go: https://saidit.net/s/AskSaidIt/comments/9y3x/anyone_else_laugh_at_the_phrase_give_yourself_a/1023g?context=3

Presuming this is the classic case of unrequited love for a woman, do the technique while thinking of the woman while performing the actions. Really think of her, like a dog rolling in mud, roll around in your every memory, impression or thought of her. Think of her tits, her smile, her eyes, everything.

Keep going until you're literally bored of thinking about her.

You're likely to find that boredom will be permanent, ie you'll be over her.

Of course this applies to other relationships, and other causes of pain, not just some woman. What it does it stimulate various nerves, similar to accupuncture, except we're deliberately breaking down the mental connections in the brain. You'll still remember her but without the pangs of pain and emotions.

Give it a go, feel free to PM