well REIT's in general are going through a volatile period, surely you have noticed... AGNC & CIM both down today as well. didn't check the others.. point is, it's not just an Apollo thing. investors are spooked until they get a better read on where the Fed (and their precious stimulus) is going.
Unlike REITs, AINV and most BDCs are less risky due to their limited leverage allowed by law (up to 1:1 debt-equity allowed by law). However, the BDC sector had increased lot last year and it has not really have a real correction yet and therefore BDCs that are traded with a high premium (way above their NAVs) and low yields such as TCAP, MAIN and TAXI will get hit hard the most in the next few months, guaranteed. No pun intended.