Can you please tell me about a bulging disc in the lower thoracic spine?

It means nothing. Bulging discs in the thoracic spine have no meaning. The thoracic spine is not mobile and much less likely to have a significant herniated disc. The presence of a herniated disc anywhere in the spine is most commonly simply part of living and nothing to worry about. The rate at which disc changes occur is largely genetic in origin. Bottom line: don't worry.