That's a tough call. I'm guessing the confidence & sparkle aspect are related to the job you do?
Can you find out ahead of time any indication of what the 'new challenges/workload' is? If yes, then use this to plan some (achievable) targets for you. If not, then get them to provide you with the 'high-level' objectives during the meeting.
Allow them to go through the whole "we've noticed x/y/z and are concerned/need you to take on more etc.,". Nod occasionally. When they are finished, reference that you'd like to have some more details on the "new challenges" so that you can come up with some targets for meeting them.
Also mention that, when you have identified possible targets, you will set up another meeting with your manager(s) to agree which of these options best meet the strategic aims of the business. Also mention that, as part of this second meeting you would like management to consider a bonus / pay rise on achieving them.
Benefits of the above approach are that without having to 'plead' you will be back to your old self soon, you have instead demonstrated you are back to your old self by:
- Driving the conversations around practicalities/business needs
- Asking for a pay rise justified by demonstrable benefit to the business (tends to be only the confident who do that!)
You may not get additional money, but that's a different conversation - and even if they say "not in the next six months due to..." it means you've left the way open to push again after that.
In terms of the 'body language' management to subtly back up your assertions:
Draw yourself up tall, go into the meeting with your shoulders' back. When you sit down, sit back in your chair, and keep your arms open on the table. This sort of posture
For the next few days, practice at the kitchen table and, in your head picture all the negatives they might throw at you. At first, you'll find your shoulders hunch when you even think what might be said. The practice gives you time to get used to pushing back to a 'relaxed but confident' posture again. In fact, even if you do temporarily hunch in the actual meeting, you can still push back to the 'confident' position.
Sorry, that turned into a bit of an essay! Just keep in mind, you will get through it. The confident and sparkling you wasn't an illusion, it's just that you've had too many things to deal with over the past few years.
Very best wishes for Friday.