Hi Maid..do you have a Dracaena 'fragrens, Corn Plant,' or Dracaena 'Janet Craig?"
The corn plant has long, pole-ish canes/trunks. Can you post a pic? Trunks of corn plants don't grow. Only the foliage.
Janet Craig's trunks grow along with the plant..After reading your last paragraph, I noticed you asked if the trunk could have grown weak, so, you probably have Dracaena 'Janet Craig.'
Though Dracaena's are considered low light plants, they do best in medium to bright light. If the trunk is thin and weak, it probably needs more light.
Place in a brighter location..a bright east is perfect, especially in summer..if you live in a cold climate, a west or south in winter will is perfect. Either direction might be too strong in summer.
I don't think the trunk weakened because of its sudden growth spurt.
You haven't added fertilizer recently, have you? If a plant is dormant, and you apply ferilizer, it'll grow taller but spindly/weak.
Which is another possibility. Your tree might be dormant right now, so don't expect much if any growth at all..Once days grow longer, you should see new growth..
Once you see new growth, add a little all purpose fertilizer..this 'might' thicken the trunk.
You said it's in an 8" pot? When was the last time it was repotted? If your plant is potbound, this will halt growing..Roots need room to spread. But only repot if needed. What state are in? Toni
My Janet Creig is about 4-5 yrs old, gets medium east light, yet still it needs repotting more than any other plant I have..

If your cane is leaning, stake it so it stands erect.

Corn plants are often grown in farms in warm, tropical climates and then shipped to the U.S.; the really thick canes are just the result of plants that have gotten all the sun, food, water, and humidity they can handle. I suspect your plant is fine, and has been grown well indoors: it's not unusual for them to put a lot of energy into root production when first purchased and then suddenly start to grow leaves much later. There's probably not that much you could do to bulk up the cane at this point, short of moving to Costa Rica (and that might not help either), but the thin cane is not necessarily a problem for the plant.