In reply to mypyrex:
Are long term investments really for you? You seem to get very concerned at every short term effect with your index linked ISA. 6 months of flatlining is very short term.
If the idea of loosing a significant fraction of your money concerns you then you shouldn't put a significant fraction into anywhere you can loose it under anything less than national financial meltdown.
If you make the mental step that you reserve a fraction of your money for risky investment (linked ISAs are much riskier if you may need the money at short notice as then you can't ride out a low), then plan your future finances with the assumption that the money is lost - or devalued in a worst case estimate, you'll stress a lot less.