Buddhist meditation is about contemplating on Dhamma which in short can be put into the Four Noble Truths.
When you are learning and practicing the noble dhamma, you are cultivating qualities such as mettā (kindness), karuṇā (compassion), muditā (sympathetic-joy) and upekkhā (equanimity). Just think practically if these are the qualities you cultivate, can they bring anything negative?
Furthermore, when one learns that this nature of Suffering (birth, aging, sickness, death, etc.) and learns that the origin of this suffering is because of the three-fold craving, and also by destroying that very same craving the mass of suffering can be removed; he or she develops this Noble Eight Fold Path which is the path leading to the cessation of that suffering.
With the development of the Noble Eight Fold Path, having removed unskilled bodily, verbal and mental actions, and contemplating on the origin and cessation phenomena, one starts to understand the dependent origination. With that you start to understand the root cause of what is arising now, and what happens if we act with lack of wise attention and lack of mindfulness. Simultaneously an unshakable Faith arises in you about the Buddha, Dhamma and the Noble Sangha (as a result of seeing the true dhamma within you). Now with that Faith and the mind fixed on Nibbana, that will become your most important protection.
When you practice dhamma this way, you don't get carried away even with highest levels of concentration or the results of such concentrations. You understand if you seek delight in them you are seeking delight in suffering.
So if you are meditating in accordance with the Noble Dhamma, only positive things can come out of that, with most positive and incomparable result being Nibbana.