I learned in general chemistry that hybridization of n orbitals produces n hybrid orbitals with the same energy (degenerate).
However, in Housecroft and Sharpe inorganic chemistry, I read the following:
The mixing of $\mathrm{s}$, $\mathrm{p}_x$, $\mathrm{p}_y$, $\mathrm{p}_z$, and $\mathrm{d}_{z^2}$ atomic orbitals gives a set of five $\mathrm{sp^3d}$ hybrid orbitals, the mutual orientations of which correspond to a trigonal bipyramidal arrangement. The five $\mathrm{sp^3d}$ hybrid orbitals are not equivalent and divide into sets of two axial and three equatorial orbitals; the axial orbital lobes lie along the $z$ axis.
The above excerpt seems to imply that the 5 resulting $\mathrm{sp^3d}$ hybrid orbitals are not degenerate and have different energies. However, this is contradictory to what I learned in general chemistry. Why is this so?