Are all our experiences transitory?
In the outer world we do not remember in detail all of our experiences. They are real for a few days and then they are totally erased because they do not stay in our day-to-day consciousness. But we keep the essence of these experiences in our inner life. In the inner world, everything is recorded permanently.
/Are the kinds of experiences that Yogis have different from those ordinary people get in life?/
Sri Aurobindo once said that the biography of a spiritual Master is all written inside. If you write the biography of an ordinary person, it can be thousands of pages long. If you want to write about his inner life, you will not be able to fill even one page. In the case of a spiritual Master, hundreds and hundreds of pages can be written about his inner life, but they are not written. A spiritual Master, who is dealing with the inner world, gives and receives hundreds of significant experiences every day. A Master's inner experiences are the predominant experiences of his life, whereas for an ordinary person inner experiences are a very rare occurrence.
/Are spiritual experiences absolutely necessary to realize God?/
No. There can be many roads leading to the same goal. One road may have many beautiful flowers on either side; another road may have only a few blooms; a third road may have none at all. If each of three seekers selects a different road according to his soul's need and preference, each of them will reach the ultimate goal.
Of course, experiences do give you additional confidence in yourself. They also give enormous delight. They encourage you and energize you to march farther and farther. And while you are having the experiences, you may feel the presence of an invisible Guide within your being, pushing you towards the light of Truth so that you may be blessed with full realization. But you can also have full and complete realization without so-called "experiences." One's expanding consciousness, as one grows into God, is itself a solid experience.