probability of this happening with normal coin = 1/1024
probability of this happening with double coin = 1

Total probability of it happening = 0.999*(1/1024) + 0.001*1 = 0.00197558593
Out of this total probability, the component due to normal coin= 0.999*(1/1024)
                               due to double headed coin: 0.001*1

Probability the coin is normal = (0.999*(1/1024)) / 0.00197558593 = 0.49382105971
Probability the coin is double = (0.001*1) / 0.00197558593 = 0.50617894408

Chance of getting heads again = (0.49382105971 / 2) + 0.50617894408

= 0.75308947393