They never left.
Other beings co-exist amongst us even today. We have just lost the ability to see them. Thankfully, we can still interact with them, but the pleasure of seeing beings, so magnificent like the Yakshis, Kinneras, Vetal etc are not going to be possible until we raise our energy levels and consciousness. The Kali yuga took away our perception and sixth sense. It is time to cultivate it again. Yes! It is possible to cultivate what we lost.
Ever hoped to see an otherworldly being? Here is the how…
Right now, most humans have their energy levels at the Muladhara or the Swadisthana. That needs to be honed and raised. Kriya yoga is the best way to raise energy levels quickly without damage to the body. There have been many such practices like the Shambhavi kriya, Mahathpranakriya etc. You cannot do hata yoga or kriya yoga from reading from a book or hearing a friend teach. IT HAS TO BE initiated by a guru. Once initiated, it is said that with powerful kriyas like the Shambavi, it takes just 6 months. Your perception blossoms and a whole new world opens up.


The scary part is that, once this level is reached, you continue seeing and living with forms that were otherwise non-existent to you. This is the reason why, as you work on increasing energy levels, your guru will let you be on your own for muladhara, swadistana and manipuraka practices. Once anahata is in focus, you cannot go on your own. The unstruck note of anahata can be heard far and wide by yakshas, devtas, dakinis, rakinis, pisachas, pretas etc. Once they come, your whole world turns upside down
You don't know if you're hallucinating, you don't know if you're awake or asleep.
It's something that will appear at your work, wake you up from your sleep or look at you all night.
Why? They are attracted to certain energy levels. The higher energy gives them hope of being lifted out of the situation they are in and the lower energy level is a calling bell to feed. They will come at once.
Also one of the reasons why your guru might hesitate to put you on anahata practice. Once mastery over the anahata happens and you taste the success of commanding these creatures, you are lost to the spiritual world