Ssushi:
Sounds like delayed muscle soreness/fatigue, a phenomenon commonly experienced by weightlifters. Anyone can experience it when the muscles have been subjected to a heavy workload, with heavy being relative to the individual's current fitness level.
Lactic acid is removed within an hour or two after cessation of exercise with no cooldown, and can be eliminated within 30 minutes or so with light pedalling, so you are not experiencing lactate buildup 2 days later.
The heaviness is due to a variety of factors. Muscles cells become strained, twisted, torn, etc. with hard riding, running, lifting, etc. Glycogen depletion and neuromuscular fatigue also contribute to the heavieness.
Additionally, you must systemically recover as well, meaning the kidneys (mostly) and the liver which have to filter an detoxify the waste generated from the workout.
Recovery is really the most important aspect of training. Everyone pushes hard, but how well do they recover???
On my favorite training ride, which is filled with national/masters champions, occasional pros, and lots of cat 1/2 riders, it's interesting to note how often the top riders show up.
The guys who are strong but usually finish in 6-15th(or worse)place in weekend races show up every tue/thurs plus they race on sat and sun.
This is a ride that goes into headwinds at 28 mph, and 35-40 mph with the wind, plus a few tough climbs. Way too much, especially for riders over 35-40 years old who work full time, have families, etc.
The national champs show up maybe once a week, sometimes once every two weeks. The guy who formed the ride years ago even commented once to a masters TT champ: "Wow you showed up twice this week!" like it was something special.
It's easy to go hard, that's what everyone does, and everyone is usually pack filler in races. The riders who win important races know that proper recovery is the only way to have top form.
We can't stop aging, but we can get more sleep, eat properly, minimize stress in other areas of our lives, etc.
If driving to work in heavy traffic stresses you out, it will effect your recovery. Instead of getting uptight about it, think about how lucky you are to be healthy enough to ride your bike when you get home.
If you are in a bad relationship, get out of it. Few things will suck the life out of you quicker that a mate who hates your sport, and complains every time you buy a new chain.
The point is, anything that causes stress in your life, mental or physical, will effect your recovery powers.
As for your workout, try to ride home from work at 85% of max hr instead of doing a trainer workout. See how long you can hold 85%. You might find you could do most of the ride at that intensity.
Try doing two days hard back-to-back and also try going hard every other day to see which way works best for you. Most riders can only fully recover from 1-3 hard workouts a week.
If you go hard two days back-to-back, do the next two days easy. 3 days hard, 3 days easy, etc. Sometimes you can be recovered but still have some stiffness in your legs which goes away after 20-30+ minutes of warming up.
Occasionally, hard workout attempts are just failures from the start, nothing goes right. If this happens, accept it and pedal easy or just go home, don't even think twice about it.
Good luck!!!