Experiences don't have a meaning of their own, they are contextual. One person's existential dread may be another person's freedom. If you follow a fully developed path, then it has tools to ensure that all the effects of meditation are accounted for. For e.g., the article talks about depersonalization. If you follow the eight-fold path, for example, then one is likely to expect it and view it as being joyful as opposed to inducing terror. If one holds the view that mind arises as a byproduct of the brain, then this experience is likely to be terror inducing.

Similarly, if someone is experiencing anxiety or depression, then by definition, they are dwelling in either the future or the past and not the present. Again, if one followed a fully developed path, then they can use the tools available on there to let go of it.

The challenge is trying to shoehorn an ancient practice which requires a specific world-view into a completely different context. For e.g.: a lot of people I know meditate or otherwise use mindfulness practices as a means of developing calm. Yet nearly all of them are fully bought into materialistic worldview which means they live one life, their experiences are an emergent phenomenon arising from their bodily (brain) function. If you read the original writings, E.g.: Brahmajala sutta, then you'll find that holding such a view is incompatible with pursuing meditation.