How can I work with doubt and existential concerns?

After a 'bad trip' a big hindrance of mine is doubt and the idea that all is just a dream that we have no control over. This brings up terrifying ideas, concepts and images for me. That this may all just be nonsense, even buddhism. I'm aware these are concepts and mental activities, but the panic that they bring on can really deter me and interfere with my practice. I fear that the Dhamma may just be a temporary fabrication of this reality that I'm in etc. The fact that I suffer and endure loneliness allows my mind to go astray. I'm not a member of any sangha and I dont get any support to continue to practice. I've suffered with misery most my life and this fact brings up many fatalistic fears. I'm wondering how I can try to start overcoming this and progress in the practice. Thanks