head over heels vs hell-bent for leather

head over heels

• Hopelessly, madly, to distraction, deeply, utterly. 

• At top speed; frantically. 

• Tumbling upside down; somersaulting. 

• Hopelessly smitten, madly in love. 

hell-bent for leather

• determinedly recklessly, in a manner that lacks restraint. 

• Synonym of hell-bent (“(recklessly) determined”) 

• Synonym of hell-for-leather (“very fast”)