anxiety or something else

Chin up. Yeah it sounds like anxiety, exactly what you described in 'it's all about what if's' is the exact description of what anxiety is. The fear of the unknown causing physical ailments. You'll get better, break ups are bad.

The sooner you accept its anxiety the quicker you can start getting over it and your treatment can start working. Take up exercise, sort your diet out get some hobbies. It'll take your mind a few weeks to get out of the routine you were in. But time is definitely the healer here.

The break up is over.

Its natural for you to feel different after 4 years of living one way...habits and all.

A break up or emotional strain is very draining.

Try very hard to live in the day...not the past or the future....Walking helps anxiety..Drinking fluids and eating and sleeping properly helps as well.

it seems like a "phase" that will pass with time...Try not to focus on the physical symptoms as much and try to carry on with JUST THIS DAY.

Breakups are very difficult. I went through such a terrible time I felt death. I never thought I would survive it. Honestly, time has healed me some and him cutting off communication. It's been years now and I'm finally trying to function as I once did. There were other factors too. It wasn't until I finally accepted the breakup and he stopped emailing me that I came to terms. So much has happened in my life but I didn't realize I had anxiety, panic attacks, and severe depression until the breakup. Now I realize I've suffered since I was very young. I agree with the other comments. ..stay busy and take it a moment at a time.

I had to accept I was stuffering from anxiety and panic attacks. For a while I thought I was physically sick.

As the others said, time will heal...