Had a good read through all the replies there, thanks for the advice all!
Been reflecting on it a bit today when I've had a moments rest, I do feel different about it now than I did last night. I'm almost certainly of the opinion that there was some logical reason it was occurring and now wish I had have just walked to the back of my garden to investigate!! But as it progressed last night it got to the stage where I was almost frozen at my back door staring at this shadow. Hindsight is a wonderful thing. At the time I thought I had did everything I could to try and figure out what it was.
The point about me being tired is a fair one, I was indeed pretty tired by that stage and have been busy lately with my head stuck in my laptop so perhaps that also didn't help. As for the speculation of me smoking a J, that definitely wasn't the case last night... Unfortunately...
As per Jamesyboyjim's advice I will keep an eye out now, just to see if anything else occurs, or maybe even have a look tonight to see if the shadow is there and to see if I can find its source. But at this stage I've just put it down to the source being unknown, rather than supernatural.
Massive thanks for the condolences too, greatly appreciated. I didn't think his death had affected as much as it has, last nights occurrences definitely made me realise just how much I'm still missing him!