Nobody has yet addressed the physical causes of feeling generalized fear. I have this problem.
On the physical level, if you have been under a lot of stress, absorbing other's energies until you are worn out, helping everyone but yourself, doing things you don't like because others want/need you to do them, putting up with toxic people, etc., you may have very depleted levels of neurotransmitters. These are the hormones that transmit messages to and from your brain and gut, and run all your body systems. Low levels can cause havoc anywhere in your body.
Left untreated, your pancreas eventually stops producing digestive enzymes and then you will not absorb nutrition correctly. In this case, it is especially protein you need to worry about, since not digesting it will make your levels of neurohormones even lower, since they are made from amino acids derived from protein. It becomes a vicious circle.
I know all this because decades of letting people use me and abuse me, which I only put a stop to recently, has put me in this position. I make such low levels of neurotransmitters that they are too low to read. This is very bad and has made me very sick and very depressed.
Drugs are not the answer, as they cause your body to think there are plenty of neurohormones, so it stops trying to make them at all. If you are already super low, they just won't work.
Lots of high EPA Omega 3 acids from fish oils, chia seeds, walnuts, etc. are needed, as well as sunshine in your eyes for at least ten minutes daily, exercise for at least 30 mns. daily (can be just a walk, out in the sun you get two for one!), getting as much sleep as you can and make sure it's deep sleep (try amber glasses if you have to get up at night, red night lights, get rid of all clocks with blue lighted numbers, try a small dose of melatonin, a large dose of L-tryptophan, etc.), and the hardest of all.....get toxic people out of your life no matter who they are, and socialize with people who lift you up only. If you are at the point I'm at, where your neurohormone levels are so low you don't want to be around other people, you have to force yourself to slowly do it.
Yes, we can pick this up from other people, but if you are feeling this way almost all the time like I am, I would look into this. Your Primary doctor can run a simple blood test if you want confirmation of your levels. The ones you want to test are serotonin, dopamine, norepinephrine, epinephrine and GABA.