PLANT PROTEST?

I have a strong, healthy, tall, very old plant sitting in a pot at the top of the stairs to my attic studio. She has plenty of light, food and care and seems happy. But lately she has begun to do something very odd: she tosses soil around.

I am not joking. Only yesterday I vacuumed around the pot where handfuls of soil had yet again popped up and sprayed the surroundings. The pot is not overly full and the compost is well patted down around the plant's trunk.
Today she has somehow, all by herself, spat out dirt again. What's more, there's a sink hole in the compost. like a hollow space under the topsoil, even though the pot is full. There are no dogs, cats, birds, mice or insects in the house.

P.S.
Since writing the above, I've figured out that what's most likely happening is that the plant's roots have grown too big for the pot, they are squeezed and thus pushing the soil up. That's why it's spilling over the rim of the pot. I've got to re-pot the plant but it's such a heavy chore, I'll have to find someone to help.