These are emergencies whatever caused them. You do not need to explain why, describe what is happening.
Convulsions, or losing consciousness and shaking. This is the reason lithium and psilocybin must not be combined, and it needs an ambulance whatever caused it.
Not a racing heart, and not the tightness that comes with panic, actual pain, or genuinely being unable to get a breath.
Together these can indicate serotonin toxicity, which is a medical emergency. It is rare with mushrooms alone and much less rare if an MAOI, tramadol or a serotonergic antidepressant is also involved.
Somebody who cannot be roused needs an ambulance. Put them on their side while you wait.
The physical risk during an experience is behavioural, traffic, water, heights, falls. If somebody cannot be kept safe by talking to them, that is a call.
Anything bought as something else, or a mushroom that might have been misidentified, changes the picture entirely. Say exactly that on the phone.
Emergency medicine treats what is in front of it. You will not be arrested for calling, and paramedics have seen this many times before. Tell them what was taken and roughly when. It changes what they do, and it is the single most useful thing you can say.
All of these are ordinary, they all end, and none of them need a hospital.
Sit with them. Do not leave them alone.
Lower the lights, turn the music off, move them somewhere smaller and quieter.
Do not argue with what they are saying. Agree, and redirect gently, “I know. Let’s sit down.”
Remind them what they took and that it wears off. They may need to hear it many times. That is normal, and repeating it is genuinely the job.
Do not give them alcohol or anything else to calm them down. Water is fine.