Sorry you are feeling so crap CC - it does sound like you have anxiety (which really means fear - fear of the future) I am no medic but have suffer with intermittent depression and anxiety. The symptoms of anxiety are many and carried but certainly feel nausea is one of them, as is difficulty in sleeping. You say you feel you are ill and you probably are, mentally rather than physically, and that makes it much harder I think especially if this is the first time you have felt like this.
Yes yoga and mindfulness are both very good, as is exercise, deep breathing (lying on back and putting hand on stomach and take a breath in and a longer one out and feel your stomach rise and fall) and distraction. However it does depend on how "poorly" you feel (this is the term medics use!) If the anxiety really is getting worse you maybe need to see a GP as there are medications that will help though only if you are really not coping.
I honestly don't think you should be going to work if you are feeling so unwell. If you had a physical illness (chest infection or tonsillitis say) you wouldn't be going to work, or even a bad dose of the flu. The problem is because there is nothing to show, we feel that we are just imagining it or making a fuss over nothing. Mental illness is very common and will affect 1 in 4 people in their lifetime.
Look after yourself - don't go to work - call in sick - you are not well enough for work, you will make yourself worse and anxiety can lead to depression and that's a real horrid illness. Try to "nip this in the bud" by taking care of yourself and seeing GP if you are getting worse rather than better. I don't think trying to go to work tomorrow and rushing to a yoga class in the evening is going to help very much to be honest.
Take care and let us know how you are.
There's a great deal of empathy on here as we all have MH problems.