Neck Coming Out!
Yes, the neck is coming out of its mortise. Get the bass to a repair person (luthier) IMMEDIATELY! Lower tension strings will help but only temporarily.
Bass strings are rarely sold to be tuned (as a normal set) in fifths! You can use a solo string on top (A), then a regular orchestral D 2nd, then tune a regular A down to G, then get a long E string (for extensions) for low C. This is one-octave below cello. It takes a bit to get used to but, yes, many players are doing this tuning now.
Best of luck!