flat for three days afterwards and I cannot work out why

We had our third evening a week ago and it went about as well as these things go. She had a good time, he was decent, nothing was awkward beyond the usual first twenty minutes.

Then Monday to Wednesday I was flat. Not sad. Not jealous. Grey. Went to work, did the work, came home, could not be bothered with anything. By Thursday it had gone completely.

The part I cannot get past is that I had prepared for two possible outcomes and got neither. I thought I would either be riding it for a week or hit by the jealousy people talk about. Instead I got nothing much on the night and three days of low afterwards, which was not on the list.

She is completely fine, which I am glad about and which also makes it harder to raise. If I tell her I have had a rough few days she is going to hear it as the evening was a mistake, and it was not. I would do it again. I just do not want to spend the following week underwater every time.

I have also not said anything because I do not want to be the reason it stops. She has been happier in general since we started this and I am not going to be the man who takes that away over a mood.

Does anyone else get the flat days rather than the dramatic ones? Does it mean something is wrong underneath that I am not seeing, or is it just what happens after a thing you looked forward to for six weeks?