2x20 and lots of sweat

After sneaking away from work early today, I had a 2x20 session planned in my head.
Set up the trainer and the paraphernalia that one needs to do a session: towels, fan, music, drinks, pulse meter etc etc.
I was still pretty warmed up from my 10 mile ride home, so i only spent a couple of minutes before I set off on session number 1: Wanted to keep it manageable, so I didn’t go out too hard. My pulse stayed quite low throughout, even though the power was ok. In the end I came in with an average wattage of 292w and an average pulse of 163bpm. Not too shabby, I thought.

A 5 minute break and I was off again. First 5 mins was ok, but it became increasingly harder to hold the same wattage. Really had to dig deep for the last 5 minutes. Came in with an average pulse of 171bpm and a wattage of 282watts.
I think this session showed up my lack of stamina. I’m ok for the first 20 mins but struggle a bit after that.