This is a great question, which often gets raised by psychotherapists, too. I guess it depends on the individual, whether this trip down memory lane inspires sweet, nourishing memories or, as you say, angst over what’s been lost. It’s quite possible that many could feel sustained by the feelings and experiences that they had long ago, without taking an emotional dive.
But since you’re doing this in a group, you’ll probably get some of each. So I suppose you could structure your imagery to be a little more protective of those who could get thrust into grief for times lost.
One thing you might do is build into the imagery something symbolic or concrete, that they could take back with them to the present from that happier (or less disabled) time. It could be a gift, some words of encouragement, a symbol of the love or happiness that was shared then… in other words, build in a “transitional object” as psychodynamic therapists like to call it – the grown-up version of a blankie or teddy bear – to have (imaginally) in the present. You’d be surprised how effective this device can be for some. (We use it in the Self-Confidence imagery and also in the narrative for Healing Trauma.)
Another thing you might do is not have them go to any unstructured place or time – just have them settle into their bodies and then be approached by a fill-in-the-blanks visitor, who offers some kind of comfort, healing, calming, acknowledgment or validation. (Again, this could wind up being someone who has died, and the risk always is that the person will start feeling sad over that loss. But way more often than not, they’ll be very happy to have had a visit from someone they weren’t expecting to see again.)
You can encourage them to stay in the moment, stick with the imagery and not pull out of it to feel grief or loss from their current standpoint. Sometimes that instruction is a big help.
But if you know of people in your class who do react this way, you can help them figure out something ahead of time that won’t generate distress.
I hope this helps.
All best wishes,