To re-express the expression \(-\sqrt{-5 - 20}\) as a complex number in the standard form \(a + bi\), we start by simplifying the square root.
First, calculate the expression under the square root:
\[ -5 - 20 = -25 \]
Now we have:
\[ -\sqrt{-25} \]
The square root of a negative number can be expressed using the imaginary unit \(i\), where \(i = \sqrt{-1}\). Thus, we can rewrite the square root:
\[ \sqrt{-25} = \sqrt{25} \cdot \sqrt{-1} = 5i \]
So we have:
\[ -\sqrt{-25} = -5i \]
Thus, the expression \(-\sqrt{-5 - 20}\) simplifies to:
\[ -5i \]
This can be expressed in standard form \(a + bi\) as:
\[ 0 - 5i \]
Therefore, the answer is:
\(-5i\)