Don, who lost his father this year, has hitherto kept his worries to himself, typically not wanting to blame professional performance on personal problems.
But, still delighted at getting back on the score sheet at Pride Park, he says:
"I hit it well but most importantly the boys got a win; I was delighted to come on, though it is frustrating being sub.
"I can understand that though; I played awful at Rotherham - I had a lot on my mind regarding family and stuff and I was pretty c**p there.
"The fans gave me stick there and I probably deserved it, and I haven't been in the side since - you have to do it on the pitch.
"It did hurt, though I got through that and it has taken a few weeks to get back in the side - now the goal might just push me back in for a starting place.
"Rotherham was one of the worst games I have played for a long time but my mind wasn't on it, because I had a lot of problems back home.
"When it is family troubles, and emotion comes into it, it is hard to play football but hopefully that is all behind me.
"My mum wasn't too well and went to hospital - it was pretty serious and all happened around the Rotherham game - but she is recovering after an operation and she is on the mend.
"I didn't sleep at all the night before the Rotherham game - and it showed the way I played on the day.
"I have also missed two and a half weeks with a calf problem that I got in Scotland, but I have trained for the last 10 days - I have been pushing hard to get my fitness.
"All I can do now is try and impress Trev; there are a couple games left before the new gaffer takes over so it is a case of trying to impress him and get a starting chance if I can.
"It is in my mind because I have been frustrated; I was hoping to have a good season this year and I would like to be starting, but the boys have had a great start and it is up to me to try and give Trevor a nod.
"I had a chat with Trev after the match on Saturday and his words when I came off the pitch were 'welcome back'.
"I know what he means because I went through a bad period emotionally so I probably didn't deserve to be in the side."
Don was an unlikely inclusion on the bench on Saturday, having been injured, and he says:
"I was a bit surprised but obviously hopeful to be in the bench; no disrespect to the lads but I didn't know if I was going to be on it."
But on it he was, and when he came off it, he grabbed the winner and says:
"I was just hoping that Kevin Horlock was going to let it go and he did; I didn't give him a call because it was really quick.
"He had a great awareness to do that because some people could have tried to flick it on, but he had the bright mind to let it go and I just hit it - you just put your foot in there and hope your technique is right on the day.
"We were never really going to settle for 0-0 but Derby played quite well and Jamo made some good saves; Conners had a few chances as well though a point would have been fair - but we did go there and nick it."
As for what his ideal position is, up front or midfield, he says:
"I don't mind; I had a chat with Trev after the Rotherham game and I said that I didn't enjoy playing out on the right - and he never picked me since!
"So I won't be asking Trev where I will be playing in the future - I don't mind as long as I play.
"I have played there for Scotland, though I am not in the latest squad; Bertie phoned me and said it would be unfair on the boys up there because I haven't played for my club.
"I totally agree with that because you have to be playing for your club to play for your country - perhaps he will ring me now! But seriously, I have the utmost respect for him."
So Don has put his cards on the table and said he wants to be regarded as an out and out striker - despite being typically modest about his abilities.
"I am not the quickest and I am not going to be doing a Jermain; I have different attributes, as I like to come in deep and try and link the play, whatever the gaffer wants to do," he says.
"I am not sure if my goal scoring record is good - I haven't checked it out but I do my best."
As for West Ham's position, he adds:
"We want to try not to be any further off the top when Alan takes over."