Separation Anxiety at 9 Years Old???

Something triggered this, in him.

Did some kids perhaps, tell stories about some kind of accident?
In the news, if your son watches the news, has he seen and heard... of any traumatic or scary news stories???
Kids this age, can and do get affected, by what other kids may be saying or gossiping about, or what they see/hear on the news, or even what a Teacher may talk about in the course of their classes.
So... ASK HIM... why he has this fear, all of a sudden.
I know you said you talked to him... about his feelings, but, what about what he could have heard, from someone else????
Or does he know anyone, who's Mom... is sick or something happened to her?

It is possible he had a friend whose mom was hurt, heard a story of someone's mom getting injured or killed, or that he had a dream where that happened to you. When we are little, we feel like our parent's are invincible and changing that paradigm can be traumatic. He may not even remember the instance that started it all.

You need to sit down and talk with him about where these fears come from and appropriate ways for him to handle it. If the anxiety continues or gets worse, take him to the pediatrician. Although unlikely, there may be a physical cause to this change in personality.

He must have overheard a news story or heard about something like this. Even studying history can freak some children out, Hearing about death, wars, accidents.

Then if they hear about a relative that is very ill, he may realize you are not invincible.

At about this age, children really do start realizing that things happen and people die.

Continue to give him opportunities to talk,

Our daughter always did best when I could find book with a subject I was noticing she was having problems with. Maybe go to a good book store and ask for help with this. Or ask his school librarian or the school counselor for some suggestions.

Many times it is an innocent misunderstanding on the child's part. They over think things they hear about or notice.

Your husband is a cop. My first thought is that he has shared either some of the things he's seen/heard or he's always saying things that cause your son to imagine what goes on out there that hubby has to deal with.. Or maybe hubby doesn't talk about what he deals with so your son's imagination is working overtime.

In my heart of hearts, I feel like this is somehow related to your husband's job and what he says or perhaps doesn't say at home.

I think it's time for a really long calm discussion... he has seen/heard something that is causing anxiety... a book/movie/tv show, something he heard on the news, something another child told him or experienced. maybe something he learned about in social studies. maybe he overheard your husband talking to you about an issue he dealt with on the job? if he can't "tell you", maybe he can whisper it to you? draw you a picture? write you a story? we all get anxious from time to time, but his anxiety seems very specific, which causes me to believe there's a direct cause for it. have you had an illness lately? any sort of medical testing? has he seen on the news about people dying from the flu epidemic this year? if you can't get anything out of him and it continues, I'd have the school counselor or another mental health professional of your choosing see if they can figure it out. and if he DOES tell you, no matter how far fetched his concern, don't "poo poo" it with "oh, that would never happen", walk through his fear with him and let him know what steps are taken to prevent whatever his fear is, and that he has a LOT of grown ups that know how to take care of him.

Did he see a scary movie or read a book where something bad happened to the mom? Is one of his friend's mom sick or perhaps been in some sort of accident? You might need to ask him specific questions to figure it out.

My first thought is he finally entered the stage of abstract thinking. Now he's being bombarded with the "what if's". This is a pretty normal thing for kiddo's to go through when they suddenly get it, that life is temporary, that they could have their world turned upside down in a flash of a gun or crash of a car or the whirl of the wind/storm.

I'm not a doctor but I'm thinking this could have several causes.

It's good to start with nice calm talks.
I'm wondering if he happened to see something about a cop, like his dad, and they to hurt or injured. He may be switching his anxiety about that to you. You might be in his mind, the only one safe for him. He's terrified of losing the one parent that's going to be there for him.

His pediatrician needs to be consulted. Could be some reaction to strep.
Or he needs a CT scan. It's such a quick change that it makes me wonder if it might be physical. But if not, ask for a referral to a counselor.

Anxiety likely triggered by something. A story he heard, something in the news or on TV, or maybe even a bad dream. What sucks is that he may not even REMEMBER what triggered it, but there's an underlying bad feeling/fear which is making him anxious.
We all suffer from anxiety at one time or another throughout our lifetimes. Most of us deal with it and it's never a real problem, but for some, it can cause periods of stress. We think of stress and anxiety as being more adult issues but it's very common in children, which kind of makes sense, doesn't it? They lack the maturity and experience to handle their irrational fears as well as (most) adults are able to do.
Just keep talking to him and reassuring him. Validate his feelings while reminding him over and over that everything will be okay. If it gets worse, or seriously starts to impact his life, talk to his pediatrician. My daughter went through a VERY hard time with anxiety when she was 12 and therapy did wonders for her.