Yes, the screen does shake when you take damage, but its magnitude does not depend on anything. For the spikes, there is actually a glitch where you take 9 HP instead of 4 because both the main player collider and ground check collider take 4 and 5 HP respectively, adding to a total of 9 HP of damage taken (can bring you from full health to half a heart). However, it is possible that only one of the colliders hit the spike, so you can take only 4 or 5 HP of damage. Thanks for the feedback!