[Jimpulse]

The jhanas were describes in the suttas. You can verify it yourself. Leigh Brasington has a lot of resources making them more accessible, https://www.lionsroar.com/entering-the-jhanas/.

I would agree that the jhanas are hallucinations and initially not subtle whatsoever. By repeated exploration of the jhanas you learn that the states are wholly dependent on many things not under your control. Application of these states in real life is a whole different animal compared to simply being able to access them as well.

* Edit: If you do decide to dive in, the first jhana can be very disorienting. It's definitely a good idea seek help in integrating the experience. Feel free to message me, and I can help or at least point you in the right direction!