I am sorry to hear you have been suffering with dizziness with no apparent cause. I am also very relieved to read that you have been thoroughly checked. There are various reasons why people experience dizzy spells and certainly stress/anxiety are one.
When we are stressed and anxious we often take shallow breaths or hyperventilate, both of which interfere with the supply of oxygen to the brain and can result in these symptoms.
Other reasons for dizziness may be dehydration, low blood sugar, lack of iron, low blood pressure and standing up too quickly, menopause (given your current age you might find it useful to look into this, or even a virus to the inner ear (dizziness often happens when lying down in this instance). Dizziness can also be a side effect of certain medications or sometimes relate to underlying health issues.
I wonder if it might help to consult with a nutritionist or medical herbalist first as they would be able to work with you in more depth to help ascertain what might be happening (www.nimh.org and www.bant.org.uk) and perhaps create a protocol to help you?
If you feel particularly drawn to explore hypnotherapy, it may help to arrange a discussion first to see if it an issue with which they are familiar? (Here is a link to find an accredited hypnotherapist : http://www.hypnotherapy-directory.org.uk).
I hope you find a practitioner who can give you some support and work with you closely to address and ease your symptoms.