My anxiety kicked in after my in-laws died. Has anyone else experienced this?

We are all going to die, and none of us know when, so there is not much point in worrying about “how many years I might have left”. However “what I haven't done, what I should have done” are things worth considering. Write yourself a ‘bucket list’ of things you want to do, keep it, and try to tick them off one by one.

Don’t worry about the after-life. If you are a good Christian, imagine going to be with God. If you have doubts about that, you won’t be able to worry when you reach peace. You will be part of the Universe, just in a different way. Love, Margaret

I too find this forum tremendously helpful in dealing with mom deteriorating mental health. It’s been a life safer!

BriBri: Perhaps a therapist would be a good fit for you at this time. After my mother passed away, whom I lived with out of state, I sought therapy including short term medication for a brief while. It helped me. Good luck. I am very sorry for your loss and send condolences.

What you are describing could be a form of PTSD
There are different forms of PTSD and there is also Stress and Anxiety.
These can effect anyone
One of the "self screening" that I found lists 17 different questions to answer. These are a few.:
Repeated, disturbing memories, thoughts or images?
Repeated, disturbing dreams?
Suddenly feeling as if the stressful experience was happening again?
Feeling upset when something reminds you of the experience?
Physical reactions, heart pounding, trouble breathing?
And it goes on.
Talking to a bereavement counselor might help. A therapist might help.
being a caregiver is not an easy task and we expect a lot of ourselves. Often to the detriment of our own health. And that is physical health as well as emotional, mental health.
Discuss with your doctor the thoughts, feelings you are having. For 2 reasons. If you need a referral for a therapist your doctor should give you one. And the stress that you are going through effects your health and the doctor needs to know what you are going through.

Of course, therapy as AlvaDeer suggested.
Having mother who since I remember was dying of every possible disease known to man (and still healthy at 80 plus)I was often full of anxiety and thinking of death.
I had to learn how to live fully. I chose to live real life.
In the meantime perhaps starting gratitude journal for every day. Small things or bigger plans for future. I plan and look up all the places I want to travel to or make a list of books I want to read this month, nothing better like getting involved in life.

We see stress of caregiving manifest in many ways. I would recommend therapy and would be you would need very little to set yourself on a path away from this endlessly circular habitual thinking. Often Licensed Social Workers in private practice for therapy are best at life transitions work. Think meanwhile of all the lives that came before you, the millions and millions who lived a life, and passed. Very few were rocket scientists! Best out to you. Get some help. This, too, shall pass.