Hi,
Today I noticed that my cactus has risen from the ground, does this mean I have to repot it? Maybe he is sick? This worries me a lot.

I think you have a problem, but it's not the pot size. If anything, the current pot looks too big. I think what is happening is that root ball of your plant is not really getting saturated when you do water, and is probably extremely dry. The surrounding soil, probably of a different nature/mix is getting wet and what you see the plant being lifted up. I would transplant it and gently loosen up that root ball, and I would put it into a smaller pot. I would not water after the transplant, just wait for it to really dry out. Good luck.

Your pot looks pretty shallow so I don't think its a problem. Ferocactus don't have taproots, instead their roots spread out very near the surface in all directions. In habitat, several feet. I do think Subtropix is right about two different soils in your pot not melding but this is the wrong time to repot if you are anywhere in the Northern hemisphere. Did you repot it? How long ago? Did you shake any of the old soil off before you replanted?

You may be able to work some of the soil out from under the plant without disturbing the roots so the bottom of the cactus is more at soil level. If you do decide to repot, wait a couple months. In the meantime, water by soaking the entire pot up to its rim to try to hydrate the soil in the rootball. Given a chance, the cactus roots will grow out of the rootball - your plant looks pretty happy so it may have already happened. But, if you can pick the plant up without pulling it up, it has not so re-settle it deeper into the pot. Don't water for a week to 10 days after you do anything to the roots.

Curious the last re-pot also.

Great advice already, but any chance a new soil/pumice mix has just settled after a few waterings?

If it's been in there a while maybe the roots are developing strongly enough to push the plant up. Doubtful but depends on the time frame.

If it's a watering issue I've had good luck soaking them (saturates whatever's in the pot), letting them drain, and ignoring them.

Learnt something new today :D

DaisyI said:

Your pot looks pretty shallow so I don't think its a problem. Ferocactus don't have taproots, instead their roots spread out very near the surface in all directions. In habitat, several feet. I do think Subtropix is right about two different soils in your pot not melding but this is the wrong time to repot if you are anywhere in the Northern hemisphere. Did you repot it? How long ago? Did you shake any of the old soil off before you replanted?

You may be able to work some of the soil out from under the plant without disturbing the roots so the bottom of the cactus is more at soil level. If you do decide to repot, wait a couple months. In the meantime, water by soaking the entire pot up to its rim to try to hydrate the soil in the rootball. Given a chance, the cactus roots will grow out of the rootball - your plant looks pretty happy so it may have already happened. But, if you can pick the plant up without pulling it up, it has not so re-settle it deeper into the pot. Don't water for a week to 10 days after you do anything to the roots.

Thank you so much for all of your replies. Answering your question, I did have to repot it roughly a year ago. More importantly, I used LECHUZA-PON culture substrate for indoor and outdoor potted plants. Also, each time when I am watering my Ferocactus I add 0.5g/1L of CACTI & Succulent. While I was repoting I did not shake any of the old soil off because there was not that much to shake off to be honest, as you know plants purchased in store are being kept in quite bad pots, and soil. Right now, I just re-settle it deeper into the pot, so I will listen to your advice and I won't be watering in the next 10 days. So, when would it be the best ti for repoting? Summer?

Thank you so much

Repot in the spring or summer, while the cactus is in active growth.