Reality is totally and utterly unique to your 'person' (for lack of a better word). Especially in the drug world. combined with high IQ and EQ doesn't help either. (For me it's even worse since i'm an empath). That's where the self doubt comes from. There is no manual or script that will give enlightement on the matter cause we are all unique. The only way is to live it, fully and unapologetically.
What i have learned is that (I'm 38, been a psychonaut for 25+ years), resisting it, will only increase the doubt resulting in certain anxiety in whatever form or shape. You gotta realise that you're battteling yourself, and become friends with the 'beast' (which is you). Embrace the doubt, and see it for what it really is: your teacher. Then, you can trick it into shaping it into whatever you want it to be (long process, consistency is key). You are your own bliss, your own doubts, your whatever. It's just one of your many facets. Combined they make you, you.
As the saying goes 'Happyness is a choice' which is utterly true. And it also applies to doubt.