Question re: muggles and dementors

[Andrew]

No: HPFGUIDX 187950

Hello, I don't post very often but something is bothering me.  I was listening to part of book 7 yesterday, the chapter where Harry went to try and get food and couldn't produce a patronus because he was wearing the locket horcrux.  It said that, although the muggles couldn't see the dementors, they could feel the despair and misery all around them.  This means that, as far as I can tell, muggles wouldn't be able to see dementors but could to some extent feel the effects of them.  Why, then, was Dudley so badly affected by the two dementors in book 5?  The effect on him was pretty extreme, more like the effect on a wizard.  Did he have some minute trace of magical blood which enabled him to see the dementors?  If the effect on Dudley was similar to the effect on a magical person, what was he experiencing when he saw the dementors?  Was his more friendly attitude towards Harry in book 7 connected with what he experienced when he saw the dementors?  I know he acknowledged the fact that Harry saved him from the dementors, but was there more to it than just that?  I'd be interested to hear other people's theories.

AJM