I'm guessing that cycling on the stationary bike could be stimulating the prostate, which can trigger sexual feelings & that could be the reason for it. Just a guess, but it's also been said that TOO much cycling can damage the prostate & also the nerves in that area & that could trigger ED issues long-term, not right way, though. I think this is mostly an issue for serious cyclists who spend long hours on the bike saddle, on the racing bikes it's a pretty narrow saddle & that puts a lot of pressure in the perineal region, leading to some nerve damage. But I'm thinking in your case a less vigorous 'massaging' of that area just kind of 'woke things up' there. Don't know if this is the case, just my guess based on my own experience & things I've read about it. I would welcome any additional comments from others, whether you agree or disagree with this...
Riding The Bike Could Simulate Sex By Doing The same repeated movement over and over again .
If You Want To Get This Feeling again then
Try Shut Your Eyes While Riding it
Try to press the pedals in the same repeated way at the same speed
Try that and comment back if it worked :-)