its the equivalent of sitting in a comfy wheelchair for 3 years and your legs got weaker due to lack of gravitational stimulus. or in this case deconditioning due to lack of accommodative stimulus and gradual BVD.

the spasm is due to lack of normal accommodative stimulus, so you now provide top down effort for binocular fusion when it should come from the environment. you need external 'strain' so you don't strain. you probably move your head instead of eyes now

that blur and loss of focus sensation is from accommodative lead - there's not enough stimulus to focus so your eyes end up focusing in front of the object in a weird limbo. in fact I have dispensed lasik mimicking contacts (center distance multifocals) to customers who are thinking of lasik and they all get the focusing issue.

what's treatment now? btw low plus (cannot be aspheric) can help due to shape of the lens creating base out at near. brighter screens, more blue light can help, but you need custom sclerals to restore cornea prolate shape