I have adhd and I get intrusive suicidal thoughts. I've found them really baffling as I've never had them when I was younger. It's come on with age and more pressure in life. I find them quite unpleasant.
Mine are hormonal and stress related, but the one thing I've found that links them is that they often come before a migraine.
That's been quite helpful for me to realise.
The cycle for me is something like:
stress = mental confusion = suicidal thoughts sometimes = headache, with suicidal thoughts sometimes
The reason that's helpful is I can see points where I can intervene.
For example, when I notice mental confusion then it's a sign of stress and means I should step back.
Likewise if I notice dark thoughts, it's a sign - time to step back.
Rather than typically what I used to think:
stress = mental confusion = there is something wrong with me, why can't I cope, beat myself up, I'm worthless etc.
Ultimately as a therapist said to me these thoughts are the brains way of preparing you to take action in the face of stress.
What I'm now trying to work out is what does stepping back in the face of stress look like.