"You should sleep."
Translation:तुम्हें सोना चाहिए।
The verb चाहना and its other forms except चाहिए always mean 'want'.
Eg: मैं बैंगलोर जाना चाहता हूँ। - I want to go to Bangalore
वह आकाशवाणी पर गाना चाहती थी। - She wanted to sing on the radio
अगर तुम चाहो तो वहां जा सकते हो। - If you want, you can go there
On the other hand, चाहिए is 'should'/'need to' (when used with a verb) and 'need' (when used with a noun)
Eg: मुझे बैंगलोर जाना चाहिए। - I should go to Bangalore
उसे आकाशवाणी पर गाना चाहिए।- She should sing on the radio
मुझे सौ रुपये चाहिए। - I need ₹100 (expresses a stronger sentiment than चाहता/want)
You can think of चाहिए as being an entirely different word which means 'need'/'should' as opposed to चाहना and its other forms which mean 'want. In general, you can't substitute one for the other.
For example, 'मैं कुछ पैसे चाहता हूँ' means 'I want some money' and there is no sense of urgency in the sentence. It is just saying that it would be nice if I could get some money at some point in the future. Compare with 'मुझे कुछ पैसे चाहिए ' which is implying that I am in need of money right now. This sentence may also be used to ask someone for money.
The difference between the two is even more pronounced when used with a verb. वह जाना चाहता है- 'He wants to go' is expressing that he wishes to go while उसे जाना चाहिए -'I should go' implies that he has an obligation to go.
Good examples! I learned this the hard way while on a loooong road trip. I was trying to use my Hindi to communicate with the other vehicle that I had to stop to use the bathroom. They took forever to stop, which I would never do to another person. It was painful. मेरी सबसे अच्छी सहेली told me the difference at that point. I'm glad to read your comment, because it reiterates and further ingrains it for me!