I take amitriptyline 10mg to help me to sleep longer, i find the best time to take it is 7pm as it seems to work for about 8hrs. It does tend to make you feel like you've got a hangover but its only a side effect & usually wears off after a week or two.

I no longer take them every night but find i can take for a week which re-sets my sleep patterns, then I take them again when i need them.

Belvederebabe- I had the jaw clenching & headaches when i started taking Citalopram but was given a gum shield to wear at night which trained me to keep my teeth apart & not grind them. As you are only taking 20mg of Amitriptyline you could be experiencing anxiety & panic as that dose is not high enough to work as an anti depressant. It would be a good idea to go back to your GP & discuss this further, they will have heard all you tell them before so do be afraid to go back, they need to help you through this.