Over the history of this forum that I have partaken in, a lot of topics have popped up about why the nose is violently swinging uo and down. Usually (If not always), here is the answer:
You’re flying too fast.
You ahould be cruising, depending on the aircraft at Mach 0.70 to Mach 0.87. To determine your Mach speed, look right below thr Airspeed gauge in the HUD. You’ll see another number like “GS ## kts.” That is the Ground Speed. Then look below that. That is your mach speed. When climbing above 10k ft. (The end of the speed restriction), I watch that gauge while I’m climbing to make sure I don’t overshoot a readonable Mach level (You shouldn’t be climbing at Mach 0.70 though…). Watch it very closely when you finally level out in cruise because that is when your Mach speed really jumps up.
You generally shouldn’t be cruising above M 0.87. For a 737, try and fly M 0.70 (This is a slow speed by the way) to M 0.78/79. For larger widebodies like the 747 or A380, try M 0.78 to M 0.87
For the record, the “M” stands for Mach and the “0.78” stands for the % of the speed of sound.
Hope this clears up confusion/helps!
Mods please delete or merge if this is a duplicate tutorial. Not sure what search terms I should use so I am relying on the ones with good memories or the other OPs about this tutorial.