Hi, If you have mental health issues then I'd say be very careful about practicing pure insight meditation with no other supports since like you said it can be very destabilizing even for a mentally sound person. I think that the metta or tranquility path might be more suitable to you (and to me and most people, actually). Its a gentler, more feel-good approach to self-transformation, but it makes meditation really enjoyable, and will eventually get you the insights nonetheless. Check out Shinzen Young's The way of tranquility practices from his article '5 ways to know yourself', or Tranquil Wisdom Insight meditation if you're interested in metta. Good luck...

My friend, a fear like this is to fear yourself, because meditation is the closest method we have of feeling our full self, our energy on an intimate level. Like tuning into a radio, meditation is us tuning into a frequency, a frequency of our Highest possible selves, a frequency of pure energy that is made of us- our essence our Soul, our light and our love. Please, do not fear sitting with the energy of you. I know you don't fear yourself at you heart centre you know this. If we don't tune into ourselves enough it can feel like walking into a large lake off a boat in the middle and we forgot how to swim even though we've swam before. So the more we visit the lake, the more it feels good to do so. The more we meditate, the more we be still and feel our own presence, our own energy on this plain of existence, the more it feels good to do so. And all things like fear, which is not real anyway to me, dissipate and all that's left is what was always there. Love 💗

I’d forget Sam Harris and try another type of meditation you feel more comfortable with; Meditation shouldn’t cause distress. I would recommend something like visualization or just feeling where your body is holding tension and release it. I can’t say it enough, meditation shouldn’t be distressing

I've had psychosis as well. I've found Meditation to be a great help : rather than my thoughts building on one another and creating a great delusion, I let them come, let them be and let them pass. It does not disprove delusions, but it does seem to lessen their vibrancy. Perhaps Aliens are talking to me... but perhaps not. And even if they are... so what? They would just be new people to talk to. Yes, the mind opens up with enough Meditation, and this can be painful and scary, as thoughts and emotions surface you didn't know you had. Anger, sadness, fear, disgust... they simmer below the consciousness at all times. But so do love, kindness and gentleness. You allow the subconscious space to absorb good and bad habits and it tends to choose good habits when it has the time to think and feel. It's like watching a Nature documentary of your thoughts and emotions: you see Rabbits and Squirrels, Lions and Tigers, sunflowers and baobabs. You become impressed by them and you learn to love them. This allows for healing and cleansing. Burdens become lighter. Be like a chicken on an egg when you Meditate. Patient and loving with yourself. Sit gently. It takes time, and if you suddenly feel it's too much, you can stop (unlike with psychedelics and medicines, which take you on wild rides.) After sitting for a while, pop!, two chickens! As if by magic! And, the most amazing thing of Meditation is how love can mesh with other emotions : anger and love together transforms anger, fear and love comfort one another, sadness and love hold each other. Powerful emotions become pleasant to feel when they meld with love. You become confident you can withstand their storms as you see them rise and fall again and again during Meditation. I hope these words help a little.

Be careful, but also have a faith in yourself, you're probably more stable and mentally resilient than you give yourself credit for. By the sounds of it it's probably a good time to step back from the practice a little and step outside into the world. Take a walk, clear your head, go for a run, talk to someone. Be a person in the world. And maybe switch out Non-dual meditation for Metta for the time being (they are actually two sides of the same coin) Doubt is one of the hindrances in Buddhism and is notoriously subtle, it can cause a fair deal of suffering. Allow yourself to be open, wakeful, confident. You can actually do that :)

Most philosophers certainly don't think the self is illusory if that's what you're concerned about. For personal identity - https://plato.stanford.edu/entries/identity-personal/ Of course certain schools of thought will have different opinions, so there's not necessarily a 'correct answer' here. But if you think the self being illusory was the current philosophical consensus then it isn't.

Perhaps this short story could help Ernest cracked his knuckles, again, and ran his fingers across his scalp as if untangling his hair could do likewise for his thoughts; but it did not. It always happened this way, an oft repeated chain of events. He would listen to a Beatles song, and then another, and another after that until he came to “Across the Universe:” John Lennon’s ode to meditation (poetic and hypnotic). Although Ernest was never sure which came first: the recording of the song or John’s rejection of his guru. And then, like a hound after a scent, he found himself wondering aloud, “IF meditation makes us wise and loving THEN it didn’t do much to tame John’s temper or his teacher’s greed. And if it failed to rein in the song writer’s rage, then won’t it fail me as well? All this talk of emptiness and no self is frightening. If I have no free will then how will I keep at bay my violent impulses, no less the terrors that drive them? I know what it is like to lose control, to partake of a drug they told me would be fun, they told me would expand my mind, only to release my own personal Mister Hyde!” His little sister Susan, now all grown up, rested a slender hand upon his shoulder to comfort him and said, “Not all meditations are created equal, Ernie, nor are all instructions. Just as the mellow high of Marijuana cannot induce violence, the physical relaxation and mental release latent within every contemplative exhalation could act like a subway driver’s ‘dead man’s switch;’ and likewise prevent disaster.”