Don't be too shocked or reactive into the prices last few days. Without seeing the full depth of the order book it's currently very open to manipulation to push prices down.
The current price is now determined by the lowest 300 shares and not the average. Using Trent as an example, he's £10 and might have 5,000 shares listed at £9.75. But if someone offers 300 at the very lowest they can it now displays his price at say £9 (maybe lower). However it's just the new 300 at this price and not a true reflection of the 5,000 at £9.75. People see this, panic and list their shares too and the price drops further. The person unliats their 300 at £9 and can now buy all the shares other people have listed for a large discount and trust that they'll bounce back. This should end when full order books are in place and you can see the full sell volume.
IPDs are also driving a lot of volatility as ppl are jumping all over to get the current promotion of x5. Meaning ppl are chasing form players and dropping anyone with a bad game. This ends in a few weeks and should hopefully calm down a bit.
Also, remember that previous profits based off market /buy now price where never real reflections as realistically you had to sell much lower. You're now seeing a more accurate display of portfolio value. I'd actually suggest that you change it further to show mid price and not top price as this is even more accurate (if initially painful).
Whilst this all sounds painful, remember it's a short term pain hopefully. Full order books will help the market grow longterm, they've just started a big marketing campaign and have just doubled dividends so hopefully it should actually be a good time right now.
If you haven't already start looking at Indexgain as they have useful info on there and even offer a free service.