These are not problems, this is a good sign. This means you are making progress :)
Contrary to the popular assumption, our mind is not supported solely by the brain. Significant parts of mind (mind is not really discrete so perhaps I should not say "parts") operates on the basis of the rest of the body. Specifically, lower layers of what's known as "subconscious mind", "emotional mind" and "intuitive mind" are in fact informational aspects of the bodily processes. Then there are currents of mind (here's a better word!) that are not confined to our body at all and are more connected with "external" processes - but that's a separate story. The point is: mind, emotions, intuition, mood, and body - are all connected in what's known as psychosomatic continuum. When you start meditating, your "conscious" layers come in contact with "subconscious" layers - and to you this looks like you suddenly discover feelings and broodings that you had no idea existed.
Specifically, some of our experiences and memories - especially powerful, traumatic and/or repetitive - are "stored" as tensions or blockages of certain muscles of the body. The most significant ones are the muscles of pelvis, abdomen, diaphragm, chest, shoulders, throat, and the muscles of face and scalp. Abdomen is where memories of danger (~fears/insecurities) are usually stored or rather the emotional components thereof.
So when you do a watching-the-bodily-sensations type of meditation long enough, eventually you open up and gain access to these somatic memories. If you keep going on in a gentle but persistent manner, you may be able to "go inside" and "dissolve" and sometimes even recollect the actual traumatic events they came from. (This second part is more like a free gift. Focusing on the recollection too much may slow down the whole process. What matters is going through the somatic/emotional bubble and opening up.) There are kilotons of energy locked up in those bubbles - and opening some of them may completely change your character and therefore the course of your life. Just be sure to proceed very very gently. Navigating these things require a lot of sensitivity. There is no danger in forcing it, it's just that being too eager makes them less likely to trust you and let you in. ("Them" being the blockages). It took you 5 months to get here, it may take you another 5 months or 5 years or 10 years to go through - needless to say it is well worth it.
A couple of auxiliary techniques I recommend:
- try to sit in a way that makes it easy to open and relax the whole area: from diaphragm to upper abdomen to lower abdomen. Start from the top or the area that you feel is the most alive and meditate on it until it starts moving and opening up. Then slowly make your way down. Keep relaxing the muscles and letting it go as you learn to trust yourself.
- on the days when you don't meditate, try to slightly tap the abdomen (like the King Kong) while making an effort to not defend it by tensing. Keep doing this very gently until you can open it up. This is really cheating and the "proper" way to do it is through Vipassana alone, but in my practice it can help speed up the process. Just don't tap so hard as to insensitize the area - overdoing the tapping may temporarily remove the physical blockage without releasing the emotional energy.
- in my experience, it helps to meditate in a very cozy atmosphere, e.g. with lots of sunshine etc. - whatever makes you feel happy, secure, and comfortable will help opening up. Sometimes you have to cultivate the positive feeling by indulging in and repeatedly enjoying whatever cues that make the ambiance look stereotypically good to you. The patterns of shadows on the wall, the rays of light, the chirps of birds - whatever works for you. Your main focus should still be on the breathing and abdomen, but let's say 20% of your attention can periodically scan the "happy cues". As with everything, don't overdo this mechanically. It's a subtle thing that requires sensitivity to what makes you happy. This is not the core technique anyway, you can achieve success with just the watching meditation alone, but it does help a bit.
This is really all there is to it ;) - just keep going and hopefully you can open your blocks and enter your subconscious through them.
There are layers beneath layers of blockages. You may open one layer only to discover another one... and another one... and another one. It does feel scary to open those - like exposing your naked soul to the world - so I understand why you're saying you feel like you need to jump off the cliff.
Finally, all of this is very individual and subjective - so your experience may not match mine, but since we are all humans we should hopefully be similar enough.