"mad" and "crazy" are perfect in almost all circumstances--laudatory,derogatory or neutral.
If you love something or somebody so much,you could say "I'm mad about it/him/her/you." or "I've gone gaga/bananas/ape/cuckoo over it/him/her/you."
For "投入" ,you might like to use "deep in" (I was deep in my studies) or "single-minded" or "dedicated" or .
"沉迷",which is connotatively negative,could be rendered into "indulge in" or "lose oneself in" or,depending on the specific situation,"overindulgence",or "obsessed with".
if you are crazy or mad about someone or something to the extent that you need to see your doctor,you could pick one from:
insane,demented,deranged,unbalanced,unhinged,lunatic,out of one's mind/head,
or one of such colloquialisms as mental,dotty,crack-brained,out of lunch,round the bend,
or one of such slang expressions as bananas (as given above),off one's head/rocker/trolley,cracked,dippy,daffy,nuts,nutty,nutty as a fruit cake,loco,up the creeks,bonkers,batty,bats,loony,screwy,gaga (as given above),goofy,balmy,flaky,moronic,cretinous,have a screw/tile loose,...
Enjoy your English.