I have the theory that, when I practice the Jhanas heavily, especially the first two, they lead to a chemical burnout, which can manifest as depression or stress. The burnout may also manifest not immediately, but the day after. This makes me less confident in actually letting go into the Jhanas deeply.

What do you think of this? I'm planning to stay for shorter periods in those first three Jhanas and best rise quickly to four. The problematic aspect is, I get stuck before reaching Jhana four sometimes. Hmh!

Hmmm, I think this is pretty atpyical because the textbook description of the jhanas is that they produce all these nice states like one pointedness, joy, bliss etc, so the pervasive sensations typically aren't stress or depression.

That being said !  I have occasionally experienced some tightness and stress in jhanas when I'm concentrating very hard.  A good way to counteract this is to relax effort a bit and let the jhanas present more naturally, even if they take more time or aren't quite as hard and stable.

I don't think you are the only person who feels this way. I have seen people use the term "jhana hangover". 

Can you go into the jhanas but not turn up the bliss to high levels? 

I find that relaxing is the most helpful thing for entering the jhanas so when I want to practice the (soft) jhanas I do a very relaxing kind of meditation, once I am very relaxed I enter the jhanas and then keep it at "entry level" because I like the pleasant relaxed feeling but not the intense bliss. It's like I push myself over the edge into the jhanas and then stop pushing, like going into a swimming pool but staying at the shallow end.  I don't find that the intense emotions are necessary to pass on to the subsequent jhanas. I just meditate on the breath at this point staying relaxed and mindful (lucid).

When I feel some type of unpleasant emotion and I am practicing the jhanas I find that it is best to relax and accept the other emotion rather than try to overwhelm it with bliss or supress it. Depending on the situation, sometimes, it fades, sometimes it is easier to bear, sometimes I just don't care that I have the unpleasant emotion - it becomes irrelevant.

I wrote this in my practice log recently:
https://www.dharmaoverground.org/c/message_boards/find_message?p_l_id=&messageId=21029479

The way I meditate to enter the jhanas is by repeating cycles of:

• Counting ten breaths while realxing and noticing the pleasant feeling of relaxation as I inhale and exhale,
• Visualizing objects each a different color of the spectrum.
• Noticing each part of the body and noticing it relaxing as I focus my attention on it

I repeat these steps until I am able to enter the jhanas.

It seems to me like trying to resist unpleasant emotions also blocks the pleasant feelings from the jhanas. Noticing, accepting, feeling fully, and relaxing into the unpleasant emotions causes the pleasant feelings from the jhanas to increase and the unpleasant emotions to be less unpleasant.

When jhana is considered as some sort of complex process rather than some fixed magical thing that when happens then it happens always the same then you can start thinking about it in terms of what actually happens in mind to make jhana in to what it is.

And one aspect of what happens is very similar to what certain drugs do. It is very possible to use up neurotransmitters when you are tripping on meditation and I experienced it numerous times.

This is pretty normal.
I would just say: carry on and try to improve it somehow as there are numerous ways it can be improved

I had this sort of burnout when I deliberately stayed in the first jhana for a long time. I also used to find that staying in the fourth too long would lower my energy levels for a day or two (even though most books say the opposite). I currently limit myself to 20 minutes of jhana time every morning and then switch to vipassana, as that seems to have the best overall outcome over a timeline of one to three days. My guess is that everyone is wired a little differently, and practices the jhanas differently, and both of those things change over time, so each of us need to adjust the dosage as we go, based on the feedback we see.

I agree, I also think diet and various fluctuating life circumstances can have an effect too.

I don't understand this but I would like to twist it into something completely unrelated and say that people should decide what they want to get from meditation and they should try to get it by practicing hard and studying different techniques, and they should not worry about what other people call "enlightenment".

Actually... you do not understand probably because it is written badly. After few re-tries I managed to decode my thoughts so the message is definitely readable.

It seems this was written in such a way that you either understand it as it is meant to be understood or it becomes scrambled mess. This is perhaps good way to write thoughts but not internet posts as people won't bother re-reading what someone wrote to get the vibe...

Words should be inviting to destination rather than just concentrating on carrying meaning over.

In order to verify your situation. I recommend you see a teacher. If you need financial assistance for a one-on-one session, let me know and we'll see what I can do!

I want to offer some other ideas in case they're helpful. My current understanding of what's going on in my own practice is that jhana is "just" relief from craving. Maybe when you sit you have the intention to just look at a feeling of e.g. lovingkindness. But craving causes distraction. The craving is accompanied by tension in the body (muscles tightening). Could be strain in big muscles like the legs, or in weird small muscles you don't even have much volitional control over, like muscles in the head. I think of the tension as being similar to what happens automatically when you are tickled, or when you bang your foot on something: you tighten up like a fist. It could be that the tightening is basically trying to keep something out, or keep something from leaving. In any case, the core of my practice is, when distracted from the object of meditation, after realizing that distraction has happened, re-smile, relax the tension, feel the relief from having relaxed, and only then go back to the object. I have a hunch that the relaxing at that crucial moment is a way of reaching back into the brain circuitry that caused the distraction and lowering its voltage, so to speak.

So the idea is, the good feelings are basically just relief from relaxing. But they are not something to be held onto tightly either. When you encounter the painful memory, maybe you see tightness in the body, and then when you consciously relax, you perceive relief from the suffering. Good. But also relax when you encounter the good feelings! I'll be relaxing, enjoying how much better it feels not to be struggling, and I'll say something to myself like "smiling with the wholesome feeling... relaaaaaxing with the wholesome feeling," as if I am offering the feeling of relief to the body, saying "look, something good is happening. When you relax, there's even more relief." Maybe you feel another subtle layer of tension fall away, and feel the tickle of even more relief. Take that feeling and do the same thing again. "See, relaxing is very good! Feel how much easier this is!" It's a virtuous cycle. Relax into things that cause you suffering, relax into things you find pleasant.