Yep. Poor Juana was head over heels in love with her husband Philip "the Handsome". He was quite taken with her at the outset of the marriage; it was one of those arranged affairs, with bride and groom being wed by proxy before ever meeting in person. When they finally did meet up, Philip was so enamored that he insisted a priest be summoned at once so they could say their vows and go to bed together. Unfortunately it didn't take him long to tire of Juana, and he turned to other women. LOTS of other women. Juana supposedly became so enraged by one of his affairs that she attacked Philip's mistress with scissors and hacked off her long golden hair. Incredible as it seems, there are actually ambassadors' despatches from the period documenting these melodramatic incidents. There may have been an element of exaggeration--I believe Philip was anxious to justify his poor treatment of Juana to her parents, the powerful Ferdinand and Isabella, whose heir Juana was. Philip no doubt wanted Isabella to believe Juana incapable of ruling, so she would appoint him to be Juana's regent in her stead. Isabella agreed about Juana being unfit to rule, but chose her husband Ferdinand to be Juana's regent, which kicked off a power struggle between the two men after Isabella died in 1504. The Castilian nobles supported Philip (they had never much liked Ferdinand but put up with him while Isabella was alive), and he reigned briefly until his death in 1506. At the time it was rumored that Ferdinand had had Philip poisoned, but more likely he died of natural causes. Anyway, poor Juana was absolutely distraught after Philip's death. At first she allowed the body to be embalmed and taken away to the monastery where Queen Isabella's parents were interred. The corpse rested there for a few months, and Juana only went to visit it once. Then she announced her intention to take Philip's body to Granada; apparently his dying wish was to be buried there. That was when things got a bit weird. She was very heavily pregnant when she set out for Granada with the corpse, and progress was very slow. She didn't actually take the body to bed with her, but she did have the coffin opened at least once so she could gaze at Philip. At one point a storm threatened, and the cortege took refuge in what turned out to be a nunnery. When Juana found out that the place was full of women she insisted upon leaving at once, supposedly because she feared they would steal Philip from her. Again, while there are eyewitness accounts of Juana's irrational behavior with regard to her husband's remains, they may have been exaggerated so as to justify appointing a regent to rule in Juana's name. Eventually it was Ferdinand who became regent for his daughter as Isabella had intended; then after Ferdinand died it was her son Charles (Carlos V) who ruled. Poor Juana didn't die until 1555; she spent nearly 50 years imprisoned in the fortress of Tordesillas by order of her father, then of her son.
No one knows for sure, but the poor lady really does seem to have been mentally ill. It ran in the family--her grandmother Isabel displayed similar symptoms, and of course her great-grandson Carlos also was insane. He was her great-grandson twice over, the child of her grandson Philip II and his first wife Maria, a Portuguese princess who was Philip's first cousin.