Exactly the same story here with 2 notable characteristics, the spiked HR which was previously unknown to me and a feeling of lactate / slight cramp in the legs even after only 10 mins of zone 2/3 cycling (used to do 3 hour rides in the past, no problem). This has all followed a flu about 6 weeks ago. I'm thinking it's definite metabolic stress caused by whatever flu has been going around that will now require a gradual and responsible build back phase, which is hard for us cyclists to do, but should be followed for safety reasons. We fix first and hopefully perform well a bit later on. Hope you return to fine form going into Summer. Take care.
