I wouldn't say you need to be symptom free, but any return to work should definitely be graded with reduced duties and hours. How reduced these need to be, or indeed whether or not you are well enough to be at work at all obviously depends on your individual circumstances. It sounds to me like if you've only just started to improve, perhaps you are not ready yet? But I don't know what your symptoms etc are.

I found occupational health very helpful in returning to work. Not only did they come up with a useful plan regarding the hours and duties I should be attempting (initially four hours per day of non-urgent desk work), the fact that they were the ones making this recommendation rather than me gave it more weight in the eyes of my managers etc.

So if you think you could do some reduced duties work then I would recommend getting yourself referred to and assessed by any occupational health department your employer may have. Once they realise that you genuinely want to work they will often be much more accommodating in terms of reduced workload than you might expect them to be. I'd repeat though that if you are not ready for it, I would not go down this road yet.

Good luck!