I would describe it differently: Psychedelics like psilocybin and LSD deactivate filters in your brain (parts of the default mode network to be precise). These filters are unconscious and do not only block weird visual effects but also thoughts and emotions. Some of the thoughts and emotions they block are scary and we probably installed those filters in our childhood during "traumatic" events but some of these thoughts and emotions were filtered because we were taught to ignore them or that they would be false or we tried things while growing up and always failed with them (not because they were impossible but due to the circumstances, e.g. parents not allowing it).
Well with those filters removed you don't only see "raw", unprocessed images, you also get all those thoughts back. Some of them can be very scary and lead you into a "bad trip" but some are also incredibly(!) freeing. And it's impossible to explain this feeling of having no mental filters to someone who did not experience it because all those filters are not conscious. You don't even know you had them until they are gone!
> Some of the thoughts and emotions they block are scary
Building on this, if someone is scared of the 'psychedelic' part then there is also MDMA which too lifts 'filters' and makes the subject aware of those thoughts and emotions so they can be processed, but takes away the fear and anxiety.
MDMA is not classified as psychedelic and currently studied for treatment of PTSD (among other diagnoses).
Psychonauts found a way to combine those effects: candyflip (a combination of LSD and MDMA) or hippieflip (psilocybin and MDMA).
Yeah, people with high blood pressure or other cardiovascular issues should be careful using all psychotropic drugs, including psychedelics - some if which are 5HT(2B) receptor agonists, and those receptors are expressed on the heart valve. But MDMA has still more dangerous physical effects than LSD/psilocybin.
Well with those filters removed you don't only see "raw", unprocessed images, you also get all those thoughts back. Some of them can be very scary and lead you into a "bad trip" but some are also incredibly(!) freeing. And it's impossible to explain this feeling of having no mental filters to someone who did not experience it because all those filters are not conscious. You don't even know you had them until they are gone!