That you are out of balance, somewhat. If you have ever studied Traditional Chinese Medicine or Ayurvedic medicine, I'm sure you know what I'm talking about.
When you acheive balance, the tingling will not be unsettling, and you should easily be able to slip past the hypnogogic imagery into a full-blown dream/ldream.
BTW - 9.5 out of 10 people here know exactly what you're talking about. He who owes nothing is rich enough.