Thankyou so much, Matt – it is so helpful of you to take the time to write a long and detailed reply. Thankyou also Loran, you both make good points.
I should really have tried to ask assistance from a teacher at my local Sangha before attempting difficult meditations, but I wasn’t sure how to broach the topic (even to my own ears, it sounds like an odd and unusual question!) or if it would be right to ask a stranger something so personal. A yoga teacher isn’t there to be my personal therapist, I guess! However, in future I will try and seek at least a little guidance from like-minded people and not get myself into unhealthy mind states through my own ignorance and poor application of techniques.
Thankyou both for the good advice! x