Meditation side effects

intense pain iln eyes, nausea and dizziness

Sounds like the effect of wrong effort or overly strenuous effort & suppression. When meditation is practised, the mind should be at ease & relaxed. The proper result of right meditation practice is calmness, called 'samatha'. When meditation is practised correctly, the mind becomes continuously aware of the natural in & out breathing, which soothes, calms & tranquilizes the mind & soul.

“dark night of the soul” and different psychological illnesses like depersonalisation

'Dark night of the soul' is fear of/from selflessness. It is something beginners to meditation & solitude experience, rather than anything "advanced".

'Depersonalisation' is liberating enlightenment. If depersonalisation becomes psychological illness then that person possibly should not be meditating. What is called 'personality' is a survival instinct created by nature. Based on the history & teachings of Buddhism, only relatively few people can peacefully attain the liberating enlightenment state of depersonalisation. This is why the Buddha generally did not teach meditation or the Noble Eightfold Path to laypeople.

In summary, the mind should feel calm & buoyant when meditating. When the mind is calm, any depersonalisation will be liberating & result in enlightenment.

I can't tell you what is the cause of the nausea but similar things can happen. One can experience unpleasant sensations while attempting to cultivate qualities and states that are good.

Lest it happens persistently it's likely not something that needs to be given much atrention.

As for the 'dark night of the soul' afaik that is terminology used on Daniel Ingram's board, not something common to Buddhist circles in general. As for depersonalization, it is also one of these terms that is very vague and not commonly used outside of that website and clinicians that for the most part have nothing to do with Buddhist studies.

Afaik it is not widely accepted that meditation causes mental illness, in general it is widely accepted that meditation does not cause mental illness.

Meditation is not something that is easy to pin down and so there are many questions about how to and about the variety of developments.

I think per definition meditation is the development of something good; not the development of mental derangement. I think people can do things that are harmful, ie they could sit cross-legged, eyes closed and contemplate the imponderables or otherwise cultivate the giving of inappropriate attention, it would be bad for them but do we call this development 'meditation'? I wouldn't.

There are four developments of Samadhi with prescribed development of perceptions, subjects for reflection and contemplation, these i would call meditation.

My question is that can an average person who is meditating for half hour or an hour a day get these side effects?

Assuming you are doing Vipassana.
Yes, any-type of experience is possible with a meditator.
It doesn't depend upon, "whether meditation is done for 1/2 - 1 hour or by seemingly average person" rather it depends upon , "how dedicatively meditation is practiced?".

You just started in car, for I started in a Bus later-on in a train. I started from 10s to 100s to 1000s of kms. journey.

Yes, symptoms remained same at start.

These were till I stopped having belly-full food during journey or before journey. Sometimes I would complete my journey by remaining hungry for 1000s of kms. and dedicatively focusing on meditation by taking adhitthana(it means to fixate your posture irrespective of room/place is shaking or not). This way, concentration increased, even the continuous noise of bus tyre or train helped me to focus on breath, sensations, seeing thoughts and analysing different sankharas through their body-effect.

Moreover, it was during journey till now, that I have made any progress in meditation.
It's just a start, don't flee away from it. Meditation is not always about merely getting calmness within 1/2 - 1 hr. It takes a lot to really calm and rectify your previous/current bad-habbits.