Here is a (practically infeasible) method to determine whether you are in a non-inertial frame of reference:
Look around you, and calculate all of the forces acting on you. The piece of lint on the floor five metres away exerts a gravitational force on you, the chair you're sitting on exerts an electrostatic force on you. That star five light years away is pulling you slightly, the sunlight shining on your face is pushing you slightly.
Add up all of these forces vectorially, and you obtain what is presumably the resultant force acting on your body, $\mathbf{F}$.
Now, compare this with $m\mathbf{a}$. If $\mathbf{F}\neq m\mathbf{a}$, then there must be 'fictitious' forces acting on you, which means you are in a non-inertial frame. For instance, the Coriolis force due to the Earth's rotation would be part of the difference between $\mathbf{F}$ and $m\mathbf{a}$.
Due to the Unruh effect (which, admittedly, has never been reliably detected in a lab), an accelerating observer sees a different particle content in the universe, compared to an inertial observer. So if the accelerating observer carries out the procedure described above, he would have new forces (due to the additional particles he observes) to enter into his calculation.
Question: Do these new forces account for the 'fictitious forces' experienced by the accelerating observer? More precisely, does the gravitational force due to the additional particles observed by a non-inertial observer account for the fictitious forces?
If this were true, then the centrifugal force experienced by someone on, say, a merry-go-round, can be explained like so: when the merry-go-round observer looks out into the universe, he observes a different mass/energy content compared to an observer standing still on the ground next the merry-go-round. The centrifugal force felt by the merry-go-round observer is precisely the gravitational force due to this additional mass/energy content. Is this understanding correct?
