That's plausable wannabe
The prosecution say that the bathroom in question was 6 meters down a passageway - does this place it outside of the bedroom in that case? Does the passageway lead just to the bathroom (effectively an ensuite then) or is it a passageway leading to the bedroom from the main house with the bathroom off it?
Reading this again, it sounds like the bathroom as ensuite - " I believed that when the intruder/s came out of the toilet we would be in grave danger. I felt trapped as my bedroom door was locked and I have limited mobility on my stumps."
If it is an ensuite I can imagine the terror could be even more ramped up - a possible intruder in such close quarters. But if he is that paranoid re security he would have surely closed the windows in the ensuite (and in the bathroom down the hall even) before going to bed? Paranoids I've known are very good at checking the things that make them feel unsafe before they are able to relax enough to sleep for example.
Then again, if it is an ensuite its an even great reason to check it's not your girlfriend simply going to the loo, when you had ample opportunity to do this by reaching out to feel her in the bed as you sorted the gun out, even though you cant see her due to pitch black. If he really thought she was in bed, why didn't he reach out to shake her awake once he had the gun, to tell her to call the police?
Another question, he has a huge home - why does he keep a cricket bat in his bedroom? Defensive weapon perhaps? It seems a strange place to keep a cricket bat though - I bet he has a whole room to keep sport kit etc.