smooth animations are overrated, just do a slideshow lol. but if u must, do what these other nerds said, onionskin or whatever and good luck with the 'not having a seizure' part

A smooth animation has flow. Don't just add inbetween frames, plan your motion paths. And keep your sprite's volume consistent unless intentional changes. Vary your timing to add interest - not everything should move on the same frames or at the same speed.

maybe post a gif? would help to actually see what u mean by having a seizure, could be too many frames too fast or too few frames too slow, hard to say without seeing the chaos

Movements looking like a seizure? A+ for realism if you're going for a horror game. Try reducing frames for simpler movements or add more for complexity, shocker, I know. Everything doesn't have to move at once, stagger those limbs.

lolz - Try to ease the motion, slow at the beginning and end, faster in the middle, keeps it smooth. Also do u use layers? Keep body parts separate, makes adjusting way easier. Just be patient it's like anything else. And backup your work, losing frames is a nightmare.

Consider learning about 'squash and stretch' as well as 'anticipation'. These principles from traditional animation are essential for breathing life into pixel art. Also, don't hesitate to use onion skinning, it allows you to see the previous and next frames so you can maintain consistency. At times even a single pixel's movement can add fluidity. Frame rate's typically around 8-12 fps for pixel stuff, experiment within that range. Also check out 'The Animator's Survival Kit' by Richard Williams, it's my bible for animation fundamentals.

haha just went through this. make sure to change stuff not only up n down but in all directions. give some anticipation before movements n follow thru after actions stop like they overshoot a bit. makes it less robot-like

Keyframes are your best friend in sprite animation. Start with the critical points of the action - the start, the mid point, and the end - then work your way with the inbetweens. Smoothness comes from easing in and out between these frames. Think about the physics behind your character's movement and let that guide how many frames you put where. Also, don't forget to drop that animation curve in when you're doing anything more complex than a basic loop!