There might be 2 things you are getting confused about so i want to make sure we are on the same page.
Collisions occur when 2 objects touch / stay touched / or seperate from each other if they have colliders and rigid bodies on them or are set as triggers.
What you are asking about is actually just a transition (MOUSE DOWN), which is something different.
From the sounds of it all you need is to put a "MOUSE DOWN" transition on your helmet object, and have that lead to your next state
try this.
make a cube. Attach a new FSM to it, and "add a transition" MOUSE DOWN. then create a second state and add the transition called MOUSE UP
then connect each state to each other.
as you hold the mouse down over the cube, it will transition to state 2, and when you release the mouse it will go back to state 1
now what "might" be happening in your case, is that you have some other events going off during a collision event eg: if your helmet falls from the sky and triggers something when it hits the ground, and is therefore taking you out of the state that is checking for that MOUSE DOWN event, so you might have to add a MOUSE DOWN event in another state if that's the case. (or you can add a second FSM to the same helmet object and take care on MOUSE DOWN events on that FSM and collision actions on the other FSM to simplify and seperate what's going on.)
hope that helps!