I’m a 26 y/o male who up to a year ago was perfectly healthy. It all started September 2017 with a couple of weeks of constipation, and several trips to the GP. After this I started to experience mild anxiety attacks, heart palpitations, dizziness and lightheadedness, chest pain that radiated around my shoulder and arm, and fatigue. This continued for months, with more than 15 visits to the GP, and a couple of visits to A&E convinced something was seriously wrong. I also noticed this slight internal tremor. On holiday in April 2018, I became more aware of a tremor in my hand, this caused me chronic stress and worry about MS, a couple of days later I went into atrial fibrillation and had to be cardioverted (quite rare for age) in a foreign hospital. Since then I have had numbness, pins and needles in my hands during the night, insomnia, muscle twitches, a resting tremor that is becoming worse, bad finger twitching. My MRI was clear, but am very worried about Parkinson’s with my resting tremor and internal shaking/vibrating. I’m sorry this is so long, any help/experience greatly appreciated!
All of what you've posted could be being created by anxiety. I've had most all of them symptoms. Constipation seems to be one of my more recent ones, rather than the first though. 
Not a doctor or medical advice. Just trying to be helpful.
Did they ever say what caused the atrial fibrillation?
Had you been on any meds prior to these symptoms? ANYTHING that you stopped up to 2-4 weeks?
Hi sam,
I get the tremor and jittery hands of I am having anxiety or if my levels of thyroid are more toward the hyperthyroidism range. I am sure they have probably checked your blood to rule out a thyroid condition though. I also had a fib but I was severely hypo thyroid st the time. I didn't have to have it corrected because once they fixed the medication I take I got better. The anxiety though gives alot of symptoms that we wouldn't necessarily even notice until we become worried about our health due to feeling poorly. Then we notice everything. We are hyper tuned into our bodies. The more worried we get the more the adrenaline flows and the more it increases our heart rate. It's very uncomfortable. Have they recommended an antidepressant or counseling. I am on my third week of the antidepressants and it is having some improvements I wouldn't say 100% yet but it's getting better then where I was. I hope you get better soon. Take it day by day and try not to worry even though it's hard. Just try to distract yourself when you start having bad thoughts. If I start to think something is wrong I just say stop and it seems to be helping right now lol.