Thank you for writing! I have a few thoughts to share with you that I hope you find helpful. 

I noticed that you said "when I get like this," which makes me think that this uncomfortable feeling is a feeling you are familiar with. When you think about the other times in your life that you felt like this, does the memory connect with a transitional time that you went through? Or flip it around- when you think back on the major transitions that you have gone through in your life, do you recall having similar feelings?

My guess is yes. The feelings that you are describing are very consistent with what many people experience during life transitions. Here are a few tips that may help you think through your current angst with fresh perspective.

1) Comfort and attachment with the familiar: 

Your discomfort currently may reflect a level of comfort and attachment to your previous situation. Change- even a positive change, is still a loss. In order to walk through a new door, we have to close the previous one. We human beings are designed biologically to bring forth tremendous adaptation amidst adversity to keep us as safe and comfortable as possible, even in environments that may not serve us well. 

Perhaps you are grieving what you let go of right now to come to this new job... perhaps you are afraid you will not find safety, comfort, and familiarty within your new envioronment. Try and remember that the same skills and resilience you used to adapt and attach to your previous job and every other new situation you have ever faced are resources still very much alive and viable inside of you. 

Not only is it normal and healthy to feel disconcerted with leaving the past behind, it actually symbolizes one of the most amazing things about life... that whatever limitations your former ____ (insert situation...job...relationship...house....circle of friends) imposed that led you to seek a new opportunity, obviously still provided value to your life, or you wouldn't be uncomfortable amidst this transition. The pain of letting it go represents the importance it played. Embrace the loss and reflect upon what it represents to you vs. struggling against it as if it has some negative hidden meaning of what's in store for you. The struggle is always in the resistance. 

2) Your strengths and resilience: 

I doubt that this this is the first hard transition that you have ever gone through in your life. What do you remember about the other transitions you have gone through in your life? The fact that you feel "awful" right now, suggests to me that you recovered from all the previous times you felt "awful" in the past, or else you wouldn't be writing to me. 

I bet that during those previous hard times, it was difficult to imagine feeling better again, but yet you eventually did. I would guess that in many cases, not only did the situation resolve itself, but it ended up with a totally different resolution than you ever would have predicted or been able to fathom prior to working through the experience. 

Our desire to know and understand when we are amidst the unfamiliar, is all about wanting to obtain a perceived sense of control. I say "perceived" because in actuality, control is almost always an illusion.  You are actually just as at risk of bad things happening in your life while working at your former job, as you are presently working in your new job. Your new job may present new and different types of risks, but on a global level, you were no more safe in the world while in your former job. 

Examining the struggle from a birds eye view like this, can hopefully assist you in shrinking down the problem from what currently feels to be near catastrophic, to a small manageable, challenge, such as "I feel like my new boss doesn't know my strengths the way my old boss did." So with that manageable challenge being identified in far more simple terms, what is your plan to help your boss get to know your work? How long does it usually take for people to get to know the real you? How many opportunities have you had this early in the game for your boss to even be able make a determination? Have you asked your boss what he or she would need from you to make you know that you are successful in their eyes? These are just a few examples of the many pragmatic and manageable elements you can choose to focus on right now, and hopefully in doing that, you will see the notable contrast as opposed to the frantic angst leading you to question your entire decision.

And finally....

3) In matters of non-life or death: 

If this was a post about a life or death matter, my advice may be different. But fortunately for you, this struggle you are going through is not one. When I was 21 I totalled my first car. I flipped it over completely and was hanging from my seatbelt when the car finally settled into a ravine in the woods. When I got out of the car, through my tears and I tried to explain to the fireman attending to me how scared, guilty, and upset I was that I had destroyed my first car. He looked deep in my eyes and said "This is just stuff, Claire. If you are still alive, you could lose literally everything you own, and it wouldn't matter. If you are alive, new stuff will always come, it will always work out." 

Point being JT, what's the worst that can happen here? If you hate your job, and you regret having gone there, you will find a new one. You will have a clearer sense of what you want and don't want from a job as a result of this experience, and will be better equipped to find the right fit next time.   If you got fired, you will lick your wounds, and you will dust yourself off, and keep going. It might suck at first, but undoubtedly, you will grow, and it will work out, just like all the other times before.

Be gentle with yourself. This too, shall pass.