What is a mystical experience according to Catholicism? After reading this about Benedict's resignation.

Benedict denied he had been visited by an apparition or had heard
God's voice, but said he had undergone a &quot;mystical experience&quot; during
which God had inspired in him an &quot;absolute desire&quot; to dedicate his
life to prayer rather than push on as pope.

I always thought that a mystical experience involves an apparition or some kind of higher state of our mind (ecstasy). I didn't think that a mystical experience can simply be some simple brain processes where we make a religious decision based on our own or circunstancial reasoning.
What is the definition of a mystical experience according to the Catholic theology? I was told that everyone is called to be a mystic. So expecting supernatural events in life should be part of our life but is that really always required?
What is a mystical experience according to Catholicism?
Sounds like the million dollar question that everyone wants to know, but is extremely hard to actually narrow down and answer.

Mystical theology is the science which treats of acts and experiences or states of the soul which cannot be produced by human effort or industry even with the ordinary aid of Divine grace. It comprises among its subjects all extraordinary forms of prayer, the higher forms of contemplation in all their varieties or gradations, private revelations, visions, and the union growing out of these between God and the soul, known as the mystical union. As the science of all that is extraordinary in the relations between the Divinity and the human spirit, mystical theology is the complement of ascetical, which treats of Christian perfection and of its acquisition by the practice of virtue, particularly by the observance of the counsels. The contents of mystical theology are doctrinal as well as experimental, as it not only records the experiences of souls mystically favoured, but also lays down rules for their guidance, which are based on the authority of the Scriptures, on the teachings of the Fathers of the Church, and on the explanations of theologians, many of them eminent as mystics. - Mystical Theology

Many Catholics consider mystical experiences uniquely a being something involving ecstasies, visions, etc. only. But in reality, it is far more complicated than that. In essence, in all revolves an individual’s level of union with God through contemplation!

In many spiritual traditions there is talk about “mystics” or “mysticism.” In the Catholic Church, this has a particular definition and describes a number of saints who are known as mystics.
The word mysticism is not surprisingly related to the word “mystery.” In this context being a mystic is automatically shrouded in mystery and is difficult to describe to someone on the outside.
On the other hand, mysticism in the Christian tradition is quite simple and in a certain sense is the goal of every Christian.
The Catholic Encyclopedia explains, “Mysticism considers as the end … the direct union of the human soul with the Divinity through contemplation and love, and attempts to determine the processes and the means of realizing this end. This contemplation, according to Mysticism, is not based on a merely analogical knowledge of the Infinite, but as a direct and immediate intuition of the Infinite.”
A mystic is someone who desires union with God and actively tries to foster that union. At times this union is miraculously expressed through spiritual ecstasies or visions, but it is not always the case. A true mystic does not seek out these extraordinary experiences, but they often occur because their heart is in such a profound union with God.
Mystics are often mysterious people as they live partly in this world, and partly in the next. Their union with God is so close that they have a difficult time remaining on earth as they desire more and more to be fully united with their ultimate love.
The Church is full of mystics and in a certain sense, all saints could be considered “mystics” in their own way. Each desired to be fully united with God and followed his will to achieve that end. Some of the more famous mystics are St. Padre Pio, St. John of the Cross, St. Teresa of Avila and St. Margaret Mary Alacoque.
In a certain sense, the goal is not to become a mystic, as if it were a title to be gained, but to achieve a profound and loving union with God. This is why we should all be “mystics” in our own way, aiming our lives to that ultimate goal that would be fully realized until the end of our life. -What is a Christian mystic?

In the end, any mystical experience is simply an experience due to a higher degree of union with God. In most cases this is simply an interior infusion of graces into the soul, accorded to certain souls closely united to the Divine Trinity through prayer, contemplation and penance.
This can be easily confirmed in the French literary works of La vie spirituelle et l'oraison, d'après la Sainte Ecriture et la tradition monastique by Mother Cécile Bruyère (12 October 1845 – 18 March 1909) which I have had the pleasure of reading several times.