It's fine. On 24 April 2015 your visa was automatically converted to a Visitor (standard) Visa.
The Visitor (standard) Visa allows the holder to engage in any permitted activity, which includes both business and tourism.
You should always carry the original documentation in preparation for your landing interview. If the IO wants to know why you didn't go the first time (which I doubt will be asked), you can simply explain it. There's really no big deal about why or why not you went the first time and since it was medical grounds, there's no point in opening up a new can of worms.
There's a somewhat related thread here: Is it easy to enter the UK multiple times on the same Business Visitor Visa?Is it easy to enter the UK multiple times on the same Business Visitor Visa?
Also related: Visiting the UK for tourism on a Business Visitor visa, after previously visiting the country for businessVisiting the UK for tourism on a Business Visitor visa, after previously visiting the country for business
You can find a complete list of permitted activities.