Here's a training drill that will serve you well when things go from bad to baddest - it's not pretty but real fighting seldom is. It's a combination of ideas I got from a post on the underground forum & some training I did with my JKD Instructor....
(Things in brackets are what you are visualising)
Take your heavy bag and lay it on the floor.
Grab it by the chains (Lapels) and drag it explosively off the floor as high as you can get it - then run with it into the nearest wall. Just let it slam against the wall & fall to the floor. (The lift is manily a conditioning element but the run & slam works!)
Drop your right knee into the bag (Sternum) and extend your left leg out to the side (Knee mount) - make sure your right foot is off the floor and all your weight is going into the bag (chest).
Grab a chain / strap (throat) and pull it down & push it into the bag so that there is some bag above it to hit.
Punch the bag as hard as you can 20 times - vary the angle of the punches, straight, hook etc (punching around his blocking hands). Punch with every ounce of strength & aggression that you have.
Hop over the bag to the other side & drop your left knee - repeat the grab & strike with your left striking.
Pick the bag up again & run/sprint to the opposite wall (you need about 5m) and repeat the drill i.e. Pickup, run, slam, knee-mount & strikes x2, until you cannot lift the bag.
This is a great conditioning drill - and will give you valuable skills that are VERY applicable to what happens in reality.
If you have a 2nd person handy - get them to grab the bottom of the bag and move it around as you are punching (opponent is squirming around under you) - you will have to use your extended leg as an outrigger to stay in the knee-mount as you wail on the bag.
This is just stage one of what we call the "knee-mount drill" - we go on to include other types of striking, armbars etc that blend into a great solo workout!
I've seen peple puke during / after their first go at this drill - it's intense!